You speak like IMAP is something as fundamental as water, it's not, it's just a protocol. And the bridge also isn't really useful on mobile, so for most of their users, it's not useful. (People using desktop email clients are a minority)
No, it may be philosophically, but in practice it's not. It may have been some time ago. Now, the huge majority uses 1. Gmail with the corresponding webapps 2. MS exchange protocol.
The only thing really fundamental to email is SMTP.
