How to prevent those people from joining? I don’t think you can.
On the other hand, Reddit communities never got that terrible, right? Not all of them at least - it’s more that the platform turned to shit. Lemmy prevents that from happening. The concept of communities moderating themselves seems to work pretty well.
Windows isn’t even that good. The OS is kind of a huge mess. It has two unfortunate advantages though: it’s the default on many devices, and (because of that) software availability is best. I wish it wasn’t the case.