Sure, any regular SME can just install Postgres or MySQL without even setting much up except with `mysql_secure_install`, a user with a password and an 'app' database. But you may end up with 10-20 database installs you need to back up, patch and so on every once in a while. And companies value that.
Cloudflare, Fly.io litestream offerings and Turso are pretty reasonably priced, given the global coverage.
AWS with Aurora is more expensive for sure and isn’t edge located if I recall correctly, so you don’t get near instant propagation of changes on the edge
The bigger thing for me is how much control you have. So far with these edge database providers you don’t have a ton of say in how things are structured. To use them optimally, I have found it works best if you are doing database-per-tenant (or customer) scenarios or using it as a read / write cache that gets exfiltrated asynchronously.
And that is where I believe the real cost factors come into play is the flexibility