People can not be anonymous through Web, so the decentralization is fake. And 98% of all Web users do not care of anonymity. For example, a lot of people use Gmail, which is not decentralized E mail service.
That makes sense actually, while we use social media platforms then we're losing our anonymity on them.
While we advocate about decentralization, we're still and will always be a customer of these centralized platforms and it's because it's just so hard to support a project that even if they say they're fully decentralized, the users won't be expanding that much for being new.
Anyway, with all of these trends, it also make sense that they're just a hype thing that contributes to the market and then eventually we see newer ones in the next year forgetting the past.