My best guess is Skype was much more profitable than MSN. But Microsoft took the best features of Skype and removed them and the quality got diminished probably in order to monkeypatch Lync into Skype as well as MSN at the time.

After like 2013 I never used Skype again. Now everyone I know either uses Discord or Slack. Teams was at least the right direction for business focus but it seems they shoulda QAd it much more. I dont hear much positive about Teams.