Can someone explain why I shouldn't just use something like cockroachdb, yugabyte or spanner for my primary database nowadays? I've seen the pain and resources wasted from teams needing to find ways to shard mysql and postgres and make them scale. Sure, you might say I might never need that scale but why not just avoid this problem entirely? If I'm building something I intend to support hundreds of millions of users why would I choose a technology I know will fail to scale to that?