A big problem here is a whole generation of developers who have learned to build stuff explicitly for AWS. If I ever inherit another Serverless project it'll be too soon.

Serverless, S3, SES, Cognito, and many many other tools are often tightly coupled to the application, so you get hooked on the "free" tier and can't extricate yourself later.

There's some hope here with Docker and Kubernetes, but a lot of companies (especially contractors) only know how to build exclusively on top of these AWS services, so if you're like most start-ups, contracting out first and second generations of your app, you can get committed to AWS for life.