Cell phones and, especially in larger cities, increased vandalism and theft of phone money boxes.
When you walked up to a phone both, and the cash box was broken open, or the cord to the handset was ripped loose from the instrument, or the glass was broken - good sign that it was no longer economically feasible to maintain the service at that location.
Fiscal prudence dictated its demise, along with the ubiquitous portable phone, no longer the size or weight of a cinder block. The cell network made that innovation even more desirable in the eyes of many, and virtually destroyed the entire landline network.
In really bad parts of cities the phone booths had broken phones in them.
That was a clue to get out of that part of town fast!