You're thinking like a nerd and not like a business person. What really happens is MySQL's main branch turns into crap, your average developer downloads MySQL because they don't know what a fork is and their boss just told them to "try this open source product". It really sucks compared to current commercial offerings because MySQL hasn't been updated in X years. Guess what just happened, unless money was an issue, they probably just decided not to go with OS.
This is what Oracle is hoping for, and imho it will happen, more-so as time goes on. MySQL may seem pretty good right this moment, but what about 2yrs from now, 5yrs, 7yrs? These forks have to make a name for themself, but chances are, the devs have either: quit the project entirely, gotten hired by Oracle and don't work on any OS code/forks anymore, or the senior devs are competiting with each other because they're all working different forks. More likely than not, Oracle has destroyed MySQL.