Why exactly do you call S3 "centralized"? You can distribute it around the world if you choose to.
Nowadays there are other companies offering S3-compatible file storage, so at best "S3-compatible" would be federated, but compared to something like IPFS that's much closer to the "centralized" end of the spectrum than to the "decentralized" end.
That is: decentralization is a separate concern from geographic distribution; the former pertains to control/ownership over the data and the hardware storing it, and in S3's case that control/ownership is centralized into a single corporation.
If somebody else could perhaps speculate about the detailed reasoning behind @sub7's claims (or even their own reasoning as to why FileCoin is a money-grab), that would also be great.