Filmmakers are particularly, but not exclusively, susceptible to this artistic pitfall. Films cost so much to make that it's much easier to do what you can sell rather than what you love. Moreover, filmmakers do not usually have the choice of starving for their art, an intellectually comforting course available to authors and painters. If you don't have film, and a camera, and lighting equipment, and sound equipment, and editing equipment, and people to run all of the above, you can't make any movie, period, and these are expensive. So, you must make what you can sell or make nothing at all.
Some filmmakers get enough clout to sell almost anything.
Some are fast enough talkers to convince others that their vision is marketable. Some are fortunate enough to have tastes conforming to those of the bulk of their days' filmgoers. Some are able to accommodate their abilities to almost anything. Some find a sympathetic patron who is either wealthy or in charge of a studio. Those who don't fit into these categories may never get to show how good they are.