I‘ve been in China from the very beginning of the Pandemic, and possibly will continue for at least one year. And for some very "prepper" accident, I personally purchased a 3M HF-52, in Dec. 2019, right before the lockdown took place.

And with quite a reasonable check frequency of the availability of the mask & replaceable filter, I can personally confirm that (at least industrial) filters have NEVER been out of stock even during Jan./Feb. 2020. A simple fact is that despite the public can retrieve knowledge from the internet that it's almost equivalent, few choose to purchase it.

In an Asian country like China where physical appearance matters most when going out to adolescents, the feeling of "standing out" might be a disaster.

When discussing it in the rationalist community, we would seldom discuss whether appearance matters in front of life risk, but this might still stand for the general public.

I can think of many reasons why elastomeric respirators haven't been widely used.

• Slow expert opinion change: airborne transmission is not significant/only cause of infection
• Bad assumptions: variants won't become significantly more contagious 
• Unfamiliarity with elastomeric respirators: no/few studies, seem too uncomfortable, some advantages aren't obvious (e.g., better face seal and comfort)
• Naive empiricism: China's lockdowns "worked," and other Asian countries (like Hong Kong, South Korea, Taiwan, and Japan) controlled covid well without respirators
• Hope: a combination of cloth/surgical masks and vaccines is good enough (see "Naive empiricism")
• Traditional expert training: contact tracing, vaccines, quarantine, social distancing
• Low death rate: there's less pressure to use the most effective means of dealing with the pandemic
• Complacency: most people that would die of covid have already died

I suspect that the main reason was that most experts thought that a combination of traditional masks, contact tracing, vaccines, quarantine, and social distancing would be good enough. Old school epidemiology and naive empiricism strongly suggested this: China's lockdowns "worked," and other Asian countries (like Hong Kong, South Korea, Taiwan, and Japan) controlled covid well with masks, contact tracing, and border restrictions but without respirators, hard lockdowns, or even vaccines.

However, in the rest of the world, these solutions weren't practical (due to the rise of more contagious variants) or available (vaccines).

1. For the record, anyone buying an elatomeric mask should get at least a P100, not anything with a "95" on it. A lot of people made that mistake. The one you suggested seems even better.
2. There are better people than me to ask about this, such as Steph Guerra. However, it's possible that, in the US, N95 masks were treated like a valuable commodity early in the pandemic and the USG bent over backwards to prevent average people from buying and hoarding them. I doubt that there were 200 billion KN95 masks in China at any point in 2020 but I might be wrong about that.
3. At some point, by summer 2022 in the US, emphasis shifted so that PPE was considered second priority to vaccination. That's where the US national security community seems to be right now, but Steph would be a much better person to ask about this, and all sorts of things related to PPE.
4. In between, there is a third thing I know of, related to contact tracing systems in China. I'm not willing to share info about this kind of thing on a public forum, but if you're interested you can DM me with more info about you, and once I have a better idea of who you are and why you might be interested, then I'd be happy to share.

I used a P100 elastomeric respirator pretty much any time I left the house, for multiple months in 2020 during early COVID, and intermittently after that.

The main downside, for me personally, was that people generally found understanding my speech through it difficult or impossible. This was a big enough problem that I haven't used one in quite some time.

Requiring more efficient masks includes admitting that the previous mask mandate was suboptimal.

It turns those people, who virtuously wear a surgical mask into people who unvirtuously do not wear the required masking.

My best guess is that Xi feels that adding a P100 mandate would be too much for the Chinese people to bear, while providing little marginal benefit on top of existing measures. It would only be worthwhile if it meant a substantial reduction in movement restrictions, testing mandates, and the amount of time people spent in quarantine and that cities spent locked down.

Xi has a policy that's working to achieve his stated aims now. The benefit of switching to a P100-based approach is hypothetical.

Plausibly, he could order a P100-based experiment in a few smaller Chinese cities. It would be really hard to know if it was working, since China currently isn't getting that much COVID. If a city switches to P100s and doesn't get COVID outbreaks, is that because the P100s work just as well, or because they're benefitting from the testing-and-lockdowns regime in the rest of the country?