Why satellites fall down to earth uncontrolablly?

It might have been pointless for lovers to wish upon a falling star last night ,because it could be a falling satellite.

Fortunately there were no casualities caused by the damaged satellite's debris, so I felt relieved.

The only question I have in mind is why satelites can't go back safely to our mother earth.
 If NASA could control the satellites properly, we do not need to worry about where they fall down.