The fact that Reddit moderators quickly folded the moment Spez threatened to take their "powers" away made the whole thing quickly fail. Very few had the balls to go through with the protests and didn't care about those imaginary powers (honorable mention to the former r/interestingasfuck mods), but many were too addicted to that fake status symbol to even imagine letting go of it and Spez took advantage of that to kill the protests.
For those of us who left Reddit and mostly only use Lemmy now, I believe the 3rd party apps thing was just the straw that broke the camel's back. I think it's just that we already hated Reddit so much that when presented with Lemmy we immediately jumped ship.
For many other Redditors however the appocalypse didn't make any difference, many big subreddits are still very active and the Reddit moderators who folded realized they don't want to lose their control over those subs and all the potential that control gives them (monetization via partnerships with brands, sponsored AMAs, selling film rights like one former mod of r/wallstreetbets did, shilling your new app, website or crypto like again r/wallstreetbets mods did etc...).
The mistake in these protests was to assume that Reddit mods would align with the interests of 3rd party app users.