Not always tastier ;) If someone can't cook!?
And not alway selfcooking is cheaper. Some canteen can cook for small money better than you could. Or if you have to buy the ingrediens but you need only small pieces of the ingredient its more expensiv.
Ok, you can use it more often, but some times you have to throw it in trash.

Drink only water instead of coffee and you will save a lot of money ;)