My thought happens to be what if a social media app management like Facebook decides to launch its own cryptocurrency? (A currency that is decentralized as Bitcoin as well as it having other properties and functions than meets the eye and qualifies as investment worthy or trade worthy coin.)
These companies you've mentioned are all centralized, thus there is no way they are going to create a decentralized cryptocurrency, let alone something as decentralized as Bitcoin, quite a lot of altcoins have tried to copy Bitcoin or claimed to be the next Bitcoin, but they have all failed woefully, mind you that altcoins hardly have any actual utility.
Having said that, as regards social media apps creating their own coins, Facebook tried something similar a few years ago with Diem coin and it was a collosal failure, it would be hard for a social media app to create something that has any actual utility or value that people would desire to use.