It's much better UX if everyone within the company uses the same office suite/email, it makes collaboration much nicer when everything is well integrated. And people get used to one system.

My guess is that having duplicate system would cost (in money for double subscriptions and lost productivity) much more than the benefit of being available 0.01% more. Especially for universities where almost nothing is really urgent and can't be delayed by a day.

Except... Outlook also has some of the worst email UX I've ever experienced