Probably accessibility. Because MySQL for some reasons is more accessible[1] to beginners, juniors, average developers, and other people who may prefer a lower

Probably accessibility. Because MySQL for some reasons is more accessible[1] to beginners, juniors, average developers, and other people who may prefer a lower barrier of entry over correctness/safety (e.g. full-stack devs, managers, people who don't have much time); who form the bulk of the community combined. It's the same for languages, frameworks, and other tech; as several people noted already. [1] Or maybe "was"; in which case the answer becomes "historical superior accessibility".