They don’t need to kill “every” lemmy/masto instance to kill the ecosystem. You just need to absorb enough of it that the only people left outside of your perversion of the ecosystem are certified weirdos.
E-Mail was (and still is) an open standard anyone could use. But after decades of getting EEE’d, you’d be hard-pressed to find someone using an E-Mail Not provided by the corporate giants, even like, other enterprises have rolled their e-mails into the Google/Microsoft ecosystems, and ALSO if you have an e-mail address that is outside those domains, normies who are inside the corporate ecosystem will have trouble communicating with you as your address will get autoflagged as spam more often than not.