I'm working on an Arduino project and I find myself wishing that I knew more about electricity. I want to know more about it, I'm genuinely curious - so why don't I still know enough? (This feeling of not understanding enough about electricity has been present in my mind for years, and also extends to other topics like math, physics, science in general, and so on.)
The thing about learning new things - and also, the thing about changing one's mind - is not so much that people are irrational and stupid. For the most part, people are actually fairly smart! It's that there is a lot of cognitive resource demand for changing one's mind, as well as for learning new things. Curiosity only gets you so far before real-life obligations pull you back. I used to have an unhealthy attitude towards people who didn't easily change their mind or who didn't learn new things all the time, looking down on them from my high plane of enlightened rationalist existence. But that's a completely wrong way of looking at things. The heuristics people use are good, they serve their purpose.
To be more clear: The bulk of the problem is not in changing one's mind. The problem is in deciding what things are important to think about. Say that you have a low-to-moderately developed opinion on some topic, e.g. nuclear power or capitalism or whatever really. Expert A comes to you and presents claims X and Y. "This makes sense", you tell yourself. You're not 100% convinced because you haven't really spent time looking into the topic. You're just acknowledging that, given that the expert's opinion is an honest assessment without bias and made with sufficient expertise, what they are saying makes sense.
Now expert B comes along and presents claims W and Z. These claims go against what the first expert said. Now you don't know anymore, but all this time you're being pulled into making up your mind, either explicitly or implicitly. But to make up your mind, first you need to decide that this is important for you to think about. And most people, completely rightfully, decide that they have no spare resources to invest in thinking about some topic. They go by rule of thumb, believe experts, accept what seems reasonable given their limited thinking about the topic, and just basically carry on with their lives. And that's completely fine. Processing power is a limited resource and it's understandable that people just don't want to think about some topic. Obviously, this presents problems if the topic is important. If you're an activist looking to change society, first you need to find ways to get people to think about what you think is important.
So, there lies the greater issue - it's not so much that people don't want to change their opinion, it's that they are solving different problems than you want them to solve. And you need to convince them to abandon a percentage of their problem-solving ability and invest it into a problem you believe to be important.
Thinking, Fast and Slow talked about the lazy thinking processes humans use, but I used to approach it with an attitude that lazy thinking was just bad and that we should all just do System 2 all the time. I never really appreciated just how many problems there are to solve in everyday life, and how much cognitive processing is required for even small changes in knowledge or opinion. Given this reality, System 1 is perfectly fine.