Connected software, with very few exceptions, doesn’t attract a very large audience. For rarer situations, you aren’t going to find that person easily. Having worldwide interest groups (like subreddits, like thematic Discord channels) helps, but is conditioned to people using either Reddit or Discord. Facebook and Instagram still win compared to those two contenders.
That’s of course assuming that Reddit and Discord wouldn’t get much bigger if Meta were to close, but I’m not sure the negative effects would vanish because the owner is different.