Scoring illegal sex along Queens’ Roosevelt Avenue has never been easier — as the number of hookers has multiplied and prostitution-related arrests have plunged by 60% along the seedy strip since soft-on-crime socialist Zohran Mamdani became mayor this year. John, a 40-year-old Manhattan horndog, said he has no problem schlepping on the subway to the notorious open-air sex bazaar — nicknamed the “Market of Sweethearts” — because the women are “cheap” and cops have their hands tied by lax laws and policies. There, scantily-clad streetwalkers brazenly solicit passersby around the clock, offering “happy ending” massages and more in front of…