Likely for security among other reasons. As soon as someone uses something like Dropbox with a weak password and it's hacked, then the university's data is out

Likely for security among other reasons. As soon as someone uses something like Dropbox with a weak password and it's hacked, then the university's data is out there or at a minimum it is perceived as the university leaking. Or a thumb drive with personal information of staff/students is lost and then leaked by the finder.