I've always wondering why, in a world where PostgreSQL exists, would anyone use MySQL I am a solid Postgres guy, but MySQL still has a better multi-master repl

I've always wondering why, in a world where PostgreSQL exists, would anyone use MySQL I am a solid Postgres guy, but MySQL still has a better multi-master replication story. Confident that Postgres will eventually surpass it, possibly even in a later iteration of 10. Now in a world where Postgres exists why would anyone use MongoDB is a valid question...