(Except for Postgres, since Fly's solution isn't managed)

Heroku's price is a persistent annoyance for every startup that uses it.

Rebuilding Heroku's stack is an attractive problem (evidenced by the graveyard of Heroku clones on Github). There's a clear KPI ($), Salesforce's pricing feels wrong out of principle, and engineering is all about efficiency!

Unfortunately, it's also an iceberg problem. And while infrastructure is not "hard" in the comp-sci sense, custom infra always creates work when your time would be better spent elsewhere.