In the bigger companies, the effort of bringing in new vendor is substantial. There are contracts that need to be approved by legal, security assessments from IT, billing arrangements from finance, user database integration, and so on. If the company already using AWS, then any product offered by AWS has a huge advantage.

I am sure that even if independent services are more loved by programmers, there will still be substantial amount of companies using AWS versions. And since the bigger companies would prefer them, I would not be surprised to know that AWS earns more money from them than startups do.