[0xy]

A lot of Netflix's technical "secret sauce" is their own infrastructure via the Open Connect initiative.

You cannot get a silky smooth experience across that many congested networks with just bare AWS.

Why would Netflix want to take on the enormous risks of self-hosting? They don't have the experience and they don't have the skills. They can hire the appropriate people but it's extremely expensive. AWS provides a lot of very valuable tooling and expertise baked into the service price.