I definitely think people without an artistic eye have a hard time making judgements on specific things like shading or linework. Also partly laziness or convenience. I have a lot of friends who go to the same guy, not because he is the best, but because he is local and someone recommended him once, so someone else went and then the rest of them. I think it can be easy especially when you are young to follow the crowd in that sense.
In terms of "good" tattoos, I certainly had a lack of knowledge before my first about how tattoos age. I don't think mine counts as good in the sense that it will stand up 20-30 years from now. Not sure if I could go back if I would change it tho, it's beautiful now.