It's expensive. Really expensive. I remember a major bank calling me and my buddy's 2-man consultancy team and telling me they had spent a small fortune on whatever the top-level access to MS developers is, to get some outdated MS COM component to interface with .NET, and MS had failed.

(We charged ~$20K and estimated two weeks. We had it working in two hours.)

I worked on a team that did. We had a monthly call with a MS rep and access to devs working on the platform features we were working on (for MS Teams specifically). It is probably more common than you think.

I remember being able to file support cases just by buying one for a couple of hundred dollars. They'd also promise that if it turned out to be a bug in the product the fee would be refunded.

(My case wasn't solved. It was something about variable delays in getting packets off the network and into userspace but we never got to the bottom of it).

I worked for a small shop that provided something MS couldn’t/wouldn’t, but which was essential for their international business anyway. So we too had engineering support.