The problem is that Task/Task<T> was the foundation for async, and it's a bad foundation. Even with the ability to write your own duck-typed awaiters (and the advent of ValueTask), the widespread use of Task means if you're writing async code you're going to have a tough time getting away from it.
Certainly the async story is a lot more complicated in desktop but it is very simple for most server scenarios, simply put "use this async call so that the thread can do other things while you wait for the db to respond" and the model in code is much preferable to callback hell.
Microsoft in general has a tendency to bolt on functionality in a kinda slapdash manner when another team wants it, so you get a lot of cruft that really doesn't belong in the Task class[1] but is there because someone wanted a way to handle their special case so it just got thrown into Task.
[1] See https://source.dot.net/#System.Private.CoreLib/Task.cs,045a7...