Nothing is stopping anyone from doing that, other than perhaps the scale.

WordPress is like 40-something% of all websites: it's the most used blog/cms/whatever platform by a huuuuge margin.

If you wanted to fork it, you'd need pretty substantial resources, a lot of committed people, and the willingness to head a giant-ass project that has millions of users, all who want different things.

It really isn't a trivial undertaking, if you're serious about it.

I would, however, expect that the big providers (Flywheel, Cloudways, WPEngine, etc.) will probably make a corpo-sponsored fork sooner rather than later, since their business depends on it, and they've got the aforementioned money and people to do it.