Influence is just not important enough that you'd want to waste it on that anyway. And why would you waste it cleaning a dorm? It's not like it's your mess or your house.
Two reasons. First, if the cafeteria worker has set off the sprinklers by burning food, the cafeteria has such a low enviro score that the sims complain regularly about it, which is annoying. Influencing a NPC to clean up all the puddles is less work than cleaning it up yourself.
Second, it annoys me when my sims either have to use a filthy toilet or clean it themselves before using it. It's more time-efficient to get an NPC to clean all the toilets if several of them are covered in radioactive green scum.
Typically I tell the cafetria worker to do it, since it avoids the 3 stooges routine of the target cleaner madly getting rid of food while the cafeteria worker rushes to replace it. Sure, it costs 2500 influence, but who cares? My sims generally have full influence meters all the time anyway. Besides influence-to-clean, the only worthwhile influence actions are "do assignment" and "write term paper." "Serve meal" would be OK if it didn't generate a plate full of useless Pepsi most of the time.
- Gus