My experience is that there are two primary factors that all bad photographers have in common...
1) They didn't dedicate their life to photography.
No man can "serve two masters" because he will inevitably love the one and despise the other. The arts do not suffer mistresses well. A photographer's "first love" must be his photography. People that try to balance their art with a day job risk the wrath of a jealous lover. The result is always the creation of work that sucks.
2) Their work is based on convention instead of self-expression.
There are a lot of photographers that fulfill the requirement of #1 and yet still consistently create bad work. They may be financially successful commercial photographers, photo-bloggers, workshop teachers or photojournalists etc. However, they've still never gotten beyond mediocre. In the arts, "good is the enemy of great" so being mediocre is just another way of saying "you suck." The reason that they are mediocre is because their work is based on convention instead of self-expression.
Convention is the opposite of originality because it can always be categorized according to a pre-existing formula. Landscape, portrait, fashion, sports etc are the conventions of photography. From the very beginning, any photographer that pursues these categories is embarking on a path that has already been taken before. He is creating work that is easily recognized and pre-judged according to the patterns that define genres. This approach may speak well to the "tribe" and even lead to financial success, but it does not speak well to the individual. Only an individual can recognize and relate well with other individuals. Art is an individual and she demands that her lover be an individual too. She will only reward those photographers that have the courage to suffer the risks of failure and alienation by peers that is required for the creation of the individual path to self-expression.
