Yeah, it's also one of the few remaining interoperable ways of communicating.

If your friend who used to use gmail is now using hotmail, you don't have to use a new app to communicate with that friend, you just update their email address and nothing else changes. If you used to be on gmail and you now want to run your own mail server you should check into a mental health clinic, but once you get out, you just tell your friends your new email address and for them nothing else changes. In fact, you can set gmail to forward emails, so any friends who forget will still communicate with you without difficulty.