Probably because the new outlook can only access microsoft servers, so they synchronise icloud to outlook server-side and you only access outlook client-side.
MAYBE give the option if for some reason I want to do it. But for it to be the default is a stupid idea. You cannot convince me there is a valid reason for this to be a thing.
I wouldn't have microsoft read my email either, of course. Thankfully in windows you have dozens of clients to choose from.
Thats what my phone does. I could have seen the value of this 10-15 years ago but I don’t see the point now.
It isn’t like this would magically get rid of the delay either, their servers still have to poll before they can send you that notification.