a] email and onedrive is not critical - for critical you better have radio and blueprints on paperself-hosting critical services
b] IT personnel is expensive and annoying, especially to females (as they treat any nerd at work as non-person)
c] cloud allows you to shift responsibility - which is kryptonite especially to middle management
d] cloud is cheaper in the short term - those who sign in will not be there when the real TC"O" arrives