Even Japanese people eat 'garbage' sushi thoughout Japan, from convenience stores etc. I don't see what the problem is.
It's like comparing McDonalds to a gourmet burger joint - the quality is obviously different but you get demand for both ends of the scale.
Whoa have you had "garbage" sushi in Japan?
It's pretty good to be honest. The quality of convenience store food, at least in Tokyo is lightyears ahead of 7-Eleven in the United States.
Also I went to a conveyor belt sushi place that charged only 120 yen per plate of 2 pieces and the quality of the rice and fish was far better than the average place here in the States where you'd spend $30-40 per person.