One aspect I haven't seen mentioned here is the economics of it. Labor rates are very expensive. A replacement carb is cheap. Why pay someone to take a carb apart, rebuild it, then put it back on when a new carb is $20 and can be replaced in 20 minutes?
That the OP had an experience where the carb was replaced and still had a problem is the result of a cheap China (Taiwan?) carb. Perhaps the shop should have known not to use such a cheap carb, but he also didn't mention whether he took it back to the shop to have it fixed properly.