If you have not experienced problems as a result of these core issues, it honestly makes me feel you must not have a lot of experience -- at least not in diverse projects and environments.

That you think picking one database is some sort of viable solution in the general case amplifies that feeling. That is so often simply not an option, and even where supporting only one database at a time is an option, you absolutely cannot guarantee that you will not have to migrate later. I've been through that pain many times, it is a real-world problem.