Could it be that people are just so used to platforms, that even in the case of the email protocol, they prefer to jump onto the Gmail platform that abstracts away from the protocol and provides a nice, easy to use platform? If so, "protocols, not platforms" remains justified, and proponents might hope that as people get more comfortable with protocols, they will drift away not only from the Facebooks and Twitters of the world, but also the Gmails.

For me personally, even if we end up with large players offering the largest (presumably most product-focused) instances of various protocols (Gmail with email, imagine Tiwtter hosting the largest Mastodon instance, Discord providing Matrix hosting), the fact I have the freedom to federate and set up my own instance or pay a smaller provider that will respect my privacy, is still a much better situation than the current "platforms, no protocols".