I think you're absolutely right that what matters is the community rather than the hosting company. But what I think the article misses is that plenty of those kinds of communities organise themselves on sites like reddit - especially since reddit was largely seeded by communities that moved over from digg, so they already know that these sites come and go. Lots of subreddits have some degree of succession plan in place, with external sites, wikis, discords etc.. Some of them already collect "best posts" into these off-reddit archives (and, sure, it's well worth reminding these communities that you need to set that kind of thing up sooner rather than later - but it's a big leap from that to "leave reddit immediately").