Well, they did get caught. But for that to happen immediately would require a detection method that can point out the presence of a farm with only a few samples. SIMs don't know their 'physical location' and triangulation of signals in these bands in the urban environment is non trivial.
Whoever did this likely isn't all that happy that their carefully created infra was used to harass officials, which most likely is the single reason this operation got uncovered in the first place. If it would have just been used for low level crime who knows how long they could have continued to do this.
Note that these are not unique to NYC or even to the United States, they've been found in other countries as well, the UK has now criminalized possession or operation of these (but the fines are so low that I don't think it will make much difference).
Whoever did this likely isn't all that happy that their carefully created infra was used to harass officials, which most likely is the single reason this operation got uncovered in the first place. If it would have just been used for low level crime who knows how long they could have continued to do this.
Note that these are not unique to NYC or even to the United States, they've been found in other countries as well, the UK has now criminalized possession or operation of these (but the fines are so low that I don't think it will make much difference).