The strongest theory I've seen for this killing reddit is that moderation quality goes down enough that being on the site is no longer fun. Even if Reddit replaces all the moderators who quit (which, yes, won't be hard), Reddit itself doesn't provide tools with the same power as what mods were using, to say nothing of the new mods' lack of experience and questionable motives and judgment (if you're smart and have good motives, you at least think really hard before going into a position left empty by mass resignation).

But yes, long term it's on We The People to fund our own communities.