Exchange is complex enough that you need a team of people to maintain it.

It’s also exposed to the internet and to end users in such a way that makes it a security target.

Keeping up with it is/was difficult, and the cost to have Microsoft do it is pretty cheap all things considered.

Every once in a while a competitor shows up but really the last competitor was groupwise.

DevOops, why break one system at a time when you can break them in batches.

Or the oh no second as Tom Scott called it.