To deorbit a satellite, you need an antenna (to receive the command), electricity (working solar panel / battery), working on board computer, fuel, correct attitude determination. So basically you need a full working satellite. As soon as one of these element fails, your satellite is dead. At 10-20 k dollars per kg, you dont want to add another satellite to your already expensive satellite.

Concerning rules, there is some progress, because nobody wants a Kessler syndrome, too much is at stake. For instance, European satellites are launched only if they naturally deorbit in less than 25 years (for LEO, of course. Above a certain height, atmospheric drag is too weak).