"Perhaps it's resentment of the widening income gap between 20-30 somethings in the tech industry and those in the service industry?"

Maybe. Because of the billionaire big winner image, people outside the industry see techies as very well off.

In fact, cops make a lot more on average -- benefits included -- than techies or programmers or engineers. In big American cities, cops are paid similar total compensation to doctors. The usual breakdown is 125k or so salary plus gold plated health care, various fancy bonuses and discounts and a pension plan that's worth more actuarially than all of the salary. Totals above $400k are not uncommon.

NYPD, as mentioned in op, is considered much more stingy than suburban NY departments so the cops in question may not be making quite that much.