Because it is cheaper to pull an IT person off from their job to do administrative or janitorial work for either short blocks of time all the time (like say 10 mins x 5 a day) or for a long block every now and then (1 day/month) than it is to hire someone at lower wages and have to cover their insurance...

Coming from someone that worked as an install tech for 18 months and spent about 1/4 of the time unpacking equipment and breaking down boxes.