If you're large enough and can negotiate appropriate contracts, it's not problem to be locked in with one vendor. Then you typically also get prices way below what's typically quoted and in line with home built.

A huge problem however for smaller companies that have little power if the vendor raises prices, discontinues products or throws them off the platform. Going all in with AWS as a small company is not only expensive but can be a risky bet.

No, they don’t want lock-in, they want the simplicity of dealing with a single vendor. It’s an important difference.

You can choose to work with a single vendor but switching to a new one should be trivial in case the prices get jacked. It’s that simple.