Other possible explanations:

• 1-bis) they taste amazing because they're new to you
• handmade cookies, when decently made, are on average better than their industrial counterparts, due to differences in the making process, and you would have appreciated most common biscuits too
• 1-ter) cooking your own biscuits prepared you to appreciate them more
• 3 bis) they are Swedish, and there are so many different kinds of biscuits recipes in the world that companies only bother to sell a handful because of specialization and standardization of tastes ; you might find your cookies in more specialized/unconventional stores, made by obscure companies
• of course those biscuits taste good! That recipe is a sugar (and butter) orgy, popular companies wouldn't sell it for fear of bad press from diabetic kids (most commercial biscuits have sugar rates between 20 and 30% which is already high, this recipe rates it at 32%, I can feel the sweetness on my tongue just by reading it)
• butter, which is used profusely in this recipe, is expensive, which would make the biscuit unprofitable if sold at market prices. Which is why high-butter rates biscuits are rare in general. Replacing milk butter with other butters significantly changes the taste.

Your recipe is gluten-free because you made it so. Any biscuit can be made gluten-free if you choose gluten-free flour, so the question 'why do companies not sell more gluten-free biscuits?' is not specific to this recipe.

Swedish perspective: It's pretty funny seeing these biscuits praised as some kind of perfect recipe/secret treasure when it's one of the most common biscuits here. And when I say common I don't mean that they can be found in stores or cafés (though they sometimes can) but that it's something many people make at home. I think the reason that they aren't more common in stores is that they taste much better when they are warm; from the oven. The stores can't compete with that.

The recipe I'm used to is pretty similar to yours (from the famous Our Cookbook) but without the ginger or salt.

I think this is almost entirely about shelf-life.

Yes, these are probably more expensive to make than Oreos, but that just means stores would stock them in addition to cheaper cookies. Some people would buy expensive-but-good cookies and some people would buy cheap-but-terrible cookies.

The problem is that the shelf-life for these is probably only a few days at best, and I doubt they'll be that much better than cheap cookies even a few hours after baking. Try wrapping some in plastic wrap and leaving them on the counter for a week and see if you'd still pay 3x what you paid for the ingredients for that cookie.

There are bakeries all over the place that sell good cookies (I'd guess about 1 bakery with good cookies per 30,000 people). But your supermarket probably doesn't stock them because of high expense and shelf life of only a few days (all that golden syrup is hygroscopic, which I suspect would be the primary culprit, though maybe fragility or the fact that real butter spoils would be more important.)

I think the comments so far are focusing too much on the biscuits, and not enough on the free market. The conundrum, after all, is not the biscuits themselves, but rather their apparently counterintuitive absence from the market.

I'm sure the biscuits are good, fantastic in fact. But the free market is absolutely inundated with food. Food is an easy problem to solve: everyone needs it and everyone likes it, and every civilization throughout history has unsurprisingly churned out thousands of varieties of it. A single average supermarket will contain thousands, if not tens of thousands, of different foods to choose from, no doubt including several hundred types of desserts and pastries. Many of these foods are outstandingly delicious, many arguably more than capable of maxing out the pleasure circuitry in the average consumer's brain.

So we can sort of shift the burden of proof: instead of asking why these biscuits aren't on the market, perhaps it's easier to ask why they should be on the market given all the other foods already there. As mentioned, it's not difficult to please consumers with food, and although each food is unique, the satisfaction and pleasure gained from it is not. Do we have any reason to believe these biscuits offer an amount of pleasure that is not already matched by 1000+ other foods already available and in mass-scale, efficient production? 

Laura made them with white flour as a breakfast. She thinks she underbaked them, I do not think this. I also had to stop her from letting them sit too long, because everyone always lets everything sit too long.

The two of us plus two kids had half of them.

My verdict is that they were a good product and distinct from the things we usually eat, and I'm happy we made them. Above average for sure, but also not the best thing in its general reference class we've made. They are not something I would want to make often, as I think repeating them would make them less tasty. 

Agree with others that these being fresh and hot added a lot (as it always does) and I expect eating them several hours or days later would not be exciting. 

Strong encouragement for others to post other such things in the future.

The most obvious explanation is that home-made biscuits are just better than industrial biscuits - due to better quality ingredients and less concern about transportation/conservation.
 

I finally got around to making these! I was very pleased with the result, they were tasty and distinct from anything I've had before. While I thought they were about as delicious as most homemade cookies, my partner who is not generally a huge fan of cookies liked them much more than previous cookie attempts and kept coming back for more. 

I agree with the other commenters who've suggested that like with most homemade cookies, they're better than store-bought cookies because they don't have to last for months on a store shelf. But I am surprised it's not a more popular home recipe in the US as it's about the easiest recipe for tasty cookies I've come across. 

The most obvious explanation is that home-made biscuits are just better than industrial biscuits - due to better quality ingredients and less concern about transportation/conservation.
 

A more practical explanation based on seeing the recipie, I'm very bad at baking, so I can't cook it:

• Too little sugar (say ~35g/100g after baking, though I will admit I'm unsure how much or into what form the heat will break down the polysaccharides in flour)
• Crumbly, how does this whole mix bind together tightly ? How will it not break into tiny pieces if transported in a truck over hundreds of km ?
• Too fat for most pallets (~22g/100g, assuming "normal' 80-85% fat butter), most people are not used to those levels of saturated fats, pastries tend to be less far and importantly the fats are mainly vegetable oils.
• Ginger is hit and miss, it's like aceto balsamico, some people add it to every dish and it makes everything better, other people hate it, little in between. So adding gingers is a move that will probably divide your audience quite heavily (as in, it's a taste boost for some, but a downgrade for others, without making or breaking the whole experience, but enough to elevate it or to turn it from good to mediocre )