As with most things, the NEC doesn't say who's going to pay for determining FOR DAMN SURE that those wires aren't being used. That's probably a lot more costly than actually removing the wires.

Imagine two single story buildings next door to one another, with two parallel driveways in between. In the 50s one company occupied both of these buildings. A 4" conduit ran between the buildings, filled with phone cables and other low voltage wiring. The buildings shared a 1A2 phone system (the old one with the row of lights across the bottom).

When I worked in one of those buildings in the 80s, the mess above the ceiling was unbelievable. It came to our attention when we heard a telephone toner through our PA system for the better part of a day.

The sound was leakage from testing in the building next door. Once management saw how many wires were just sitting above the ceiling -- in this building they had been leasing for twenty years -- they gently backed away and and waited for the toner to go quiet.

Who the hell was going to pay for wire removal? Nobody.