It works because if you are already using a bunch of AWS services, and then you need something that they are providing, you will give that a go first. If it doesn't provide enough, you will move to something else.

Many, many projects, will meet business or contract requirements with the lowest friction product. A great example is "IDS/IPS" or "Anti-malware". Unless specific metrics, requirements, or fine/fee structures exist, 9/10 times, people will check the box on the easiest to deploy.

This is a broad statement :-)

Compliance is mandatory and often sales advantage for being able to sell to certain class of enterprises.

IMHO, quality vs. rich feature set are different things and I see that being mixed up in the overall discussion. All AWS services exceed certain quality standards. Services are built to solve customer problems first. It's not unusual to find gap in feature set vs. competition.

Disclaimer: I used to work for AWS, but do not work there anymore.

This is pretty much spot on.

We use a ton of AWS's services because AWS is already on-boarded for our enterprise. It's way easier to use a AWS feature than to on-board a specialized vendor.