For a lot of companies, switching databases is effectively impossible. Perhaps not quite as impossible as switching game engines, but certainly impossible enough that it would kill the business. A lot of companies use database specific functionality that's far from trivial to replicate in another database. A lot of that database specific functionality can also be legacy that no one really understands anymore. Migrating without an option to keep these poorly understood but critical systems will set you up for unexpected data loss, corruption or availability issues. And that's after spending a year on your migration. If Oracle pulls anything like Unity here, this will kill off a lot of companies
I'm just saying it's not as bad because it's quite a bit easier to switch a database than to switch a game engine.