The difference being that Oracle getting itself into an unrecoverable state is really really rare whereas MySQL corrupts data at the drop of a hat. Seriously, even Monty himself has blogged about it.
Supporting your own database effectively means writing your own database. Once you start hacking at it to fix a problem it's a fork and you're on your own. Any organization that puts its eggs in one person like this is bonkers.
There are tens of thousands of organizations that disagree with you. I bet that most of them don't fork MySQL when they hit bugs (assuming they do hit bugs).
I'm not claiming that MySQL is perfect (or even good), only that many organizations think it's good enough, and are willing to take that risk.
Supporting your own database effectively means writing your own database. Once you start hacking at it to fix a problem it's a fork and you're on your own. Any organization that puts its eggs in one person like this is bonkers.