Why is there no begging in Japan, despite the Buddhist custom of monks begging and the large number of homeless people?
Not sure. If you do see what looks like a Buddhist priest standing outside touristy places like Ryogoku sumo stadium Japanese people assume they are fakes because they know how well off the average Buddhist priest is. The way the homeless make sure they look clean and their “homes” look nice and are far from the crowds suggests they might be too ashamed to beg. Alternatively, maybe the authorities just stamped it out at one point and it never came back.