The major players tried teaming up 12 years ago but it didn't work out: https://en.wikipedia.org/wiki/WebScaleSQL

The general response from the community often included complaints of there being too much fragmentation / too many forks, and that situation has only gotten worse since then.

Also MariaDB looks increasingly well-positioned to gain marketshare. They're making some strategic steps to improve MySQL compat and ease-of-migration.