Buildings with modern working sprinkler systems are rarely an issue for firefighters. As for break-ins the concierge rarely let roving bands of hooligans in to trash places / squat.
Empty luxury condos are not the fire / squat hazard that abandoned warehouses, etc are. Nice try.
It's pretty likely that someone would notice a squat in a luxury condo.
As for city services the NYPD could probably greatly improve their budget by not unconstitutionally stopping and frisking people.
The city costs money to run regardless, and the people buying crashpads there still want it to be the NYC they bought into when they end up sleep there.