I'm a sysadmin and have run schools on bare metal and on cloud. There are things like drive failures, hardware failures, connectivity issues, networking, user access, and all of those things that are much easier in the cloud. Much easier to spin up or down if you no longer need them.
If you're running networked storage, then that needs to have both a fail-over node and backup solution. You probably need to run extra hardware, cabling, etc. Cloud trivializes this.
If you're saving 15k in terms of hard cost, but spending 55k/yr for a sysadmin on-prem to maintain, then you're not saving money at all.
A disaster can be as simple as a failed disk, or overheated server because you're not a sysadmin and you put the server in a cabinet (I've run into this, dealing with faculty). Dead computer, no lessons for the week - lost time for the school and the professor in question.
Every place is different; you have to do a cost analysis and it's not as simple as "I saved 10x!"