Why do “suits” who are high-volume email users prefer Outlook over mutt?
Mutt is powerful. (Even though it has no nice website).
To know the power one need to learn.
Suites don’t have time for learning. (And use Windows, ahhh.)
Give me few hours with any of them, and there will be efficiency demonstrated like they have never seen before. All by using mutt email client. Including any kind of calendaring, reminding, and so on.
P.S. Outlook is Windows thing, mutt is rather GNU/Linux and Unix-like thing and this is the main reason why™.