Why were the friend notifications removed?

Was on the phone with Microsoft for an hour yesterday and after two transfers I was finally able to talk to someone that knew what I was talking about. They said Microsoft is aware of the issue... Amazing that it takes this long when so many people are having the same problem.

They weren’t removed, they just haven’t worked in 2 weeks and they haven’t fixed it yet and probably won’t for a while since only bots respond on here telling us the same trouble shooting options that aren’t gonna work because it’s not on our end but Xbox’s end

I don’t think they were removed, they just haven’t been working for a few weeks now. Hopefully it gets fixed soon, Microsoft hasn’t addressed the issue yet. It’s definitely an issue on their end since it’s happening to everyone.

I'm not sure what you mean, you can adjust which notifications you receive in your account dashboard on the Xbox, Including Friend pop-ups

No. The feature was re-enabled which is why the notification was removed.