1) The general public, including the masses who helped make TNG one of the most popular shows of its time, didn't watch DS9, and had no clue what the Dominion War was.
2) Paramount didn't allow for big Trek movie budgets.
3) It'd have been very difficult to align a feature, which can take years to produce, with a series churning out sixteen or so hours of content (not counting commercials and credits) every year.
all very good points.
INS went the right route in not telling a Dominion war story. Unfortunately, crappy writing sank the movie, not the idea to ignore the war.