Because generally speaking SQL databases don't work well with serverless and are a pain to distribute geographically.
A pain to distribute geographically? What do you think big enterprises and banks use? Oracle or Mongo? If by “a pain” you mean “not free” then you’re right. Depends on how valuable your data is and how much you care about integrity.
Also I’m not a big enterprise nor a bank.
Edit:
IIRC I read that each connection to Postgres consumes 10MB or RAM.
https://www.postgresql.org/message-id/flat/20200301083601.ew...
Maybe the proposal above by itself isn't enough, but it's going to solve some of the many problems that put a restriction on max allowable connections in the first place. For example, I am not sure if there is anything in there to reduce the baseline per connection memory consumption, but maybe that will come up as the next problem to solve and will hopefully be solved sooner than later.
To me, data has "live" somewhere. When one computer is storing that and serving it, it is by definition a server.
Is there something I've missed??
Cloud functions are triggered on demand so these scale up and down as needed.