That's the whole point of the argument as long as there is Mozilla nothing new will come because there is Mozilla. That's why Google is still funding them.
What's stopping people from working on another project? We have Ladybird [1], but it's still a work in progress. There are also LibreWolf, Icecat and other forks of Mozilla Firefox.
As if writing a browser and an email client is a piece of cake and there are tons of alternatives ready to take over. Blink and WebKit don't count.
That's the whole point of the argument as long as there is Mozilla nothing new will come because there is Mozilla. That's why Google is still funding them.
What's stopping people from working on another project? We have Ladybird [1], but it's still a work in progress. There are also LibreWolf, Icecat and other forks of Mozilla Firefox.
[1]: https://ladybird.org/