Could you imagine when one of those people get a fish on the line, and the fish moving around in the water, how tangled the other peoples lines will get it
I remember when I was a bit younger, there were a few local fisherman on the nearby bridge with all of this gear on huge tackle boxes out etc. They had nothing. I walked down on top of some rocks reached my hand down and picked one of the big rainbow trout right out of the water. There were like 3 fat ones well over a foot long and I grabbed a stick and pulled another one right towards me, it was hilariously easy to grab ahold of them. I tossed the one back in because I don't eat fish and didn't care. I couldn't imagine how many others I could have grabbed if I went into the water and actually tried to catch more. I think one of the guys was yelling out "grab it, grab it" or something rather, it was funny.
I don't know what the NYC law is about fishing from bridges but before the construction of the new City Island bridge, you couldn't go under it in a boat without a fishing line getting tangled on the boat.