Greed: Don't fix the copper wire infrastructure we get paid to maintain.
Control: If you're moved off of copper wire POTS, then in an emergency or power outage you cannot effectively call for help. Wireless systems get overrun with numbers of calls if the emergency is large enough (hurricane, tornado, flood, etc) and your call will not get through. Or you won't have power (wireless), whereas copper is designed to (almost) always have power and JUST WORK.
Power: See above. Put on your tin foil hat, but this is one step in a wave to disrupt and control communication when a "state of emergency" or "martial law" is declared. Just wait.