Larger companies have also been known to buy out critical service vendors and in-house them when there was a risk that they might otherwise shutdown or pivot, too; that's less often an option fot smaller firms.
The objection here isn't to hosting per-se – most companies aren't in the business of maintaining PostgreSQL and should consider outsourcing that task early on. If your host of choice shuts down, that's a standard service, you can dump and restore your DB and move on. Annoying but NBD.
The danger with jamstack or BaaS or similar approaches is working yourself into a place where a proprietary service API is baked into your product as a critical, fundamental dependency; if and when the host shuts down, you're in extreme trouble. That's what I'd heavily caution against.
(There's an argument that when the proprietary service is run by an MS or AWS or Google "they won't go bankrupt" so there's no risk, but even then those companies shift priorities and shut down services not infrequently).
Which is to say, you wouldn't have heard of them, because they never got big enough to be known to anyone beyond a handful of clients and employees. I've personally been hired to try to rescue such a company, and was not successful.