This is usually not because the artists involved are bad at what they do, but one or both of: deliberately catering to "bad" taste that is nonetheless popular, or making work worse than it could be to make the cost/demand curve line up better by saving some money on aspects that won't make more money if they're better (see: the MCU, which I actually like but which definitely avoids risks that might improve their films, and cuts corners in ways that don't matter much for the bottom line); or, organizational/managerial failure on projects that require large organizations to attempt in the first place (film is especially prone to this).