That's true the way you say it, and that's definitely the problem that `getrandom()` solves by blocking if the random pool isn't initialized yet. But a lot of people take that to mean "you should never get more than N random bytes from a pool that has N bytes of entropy", and that part is wrong.

All of crypto relies on being able to generate an arbitrary amount of good random bytes from a single 256-or-whatever-byte seed. Otherwise it wouldn't be safe to encrypt a long message with a short key.