I think I've seen the term "trust moat" used before, which I like for describing this effect.
Do I trust a new service or continue with one of the most trusted service from AWS?
I think that honestly, the biggest sell for a lot of newcomers is gonna be "you don't need to know AWS!" -- in my (very limited!) experience, if you want to do X with AWS, you're gonna need to learn how to do W, Y, Z, and maybe A and B with AWS too.
AWS moves so quickly I think it would be a disadvantage to rely on a smaller, unknown 3rd party that tries to replace itself as AWS.