If a movie is rated R, it generally will need a MUCH smaller budget than a a PG-13 one would in order to turn a profit. The trend seems to be that when an R-rated movie turns a profit, it has had a pretty small budget (comparatively to others). A D&D movie that had been made for 50 million would have probably made a profit with the box office of HaT for example, or even a smaller Box Office if HaT was R-rated.
I don't feel that a D&D movie should be R-rated, but I think it should have gone more towards the route which those outside of the hobby may view D&D. This would actually mean more of a turn towards more traditional characters of more general Tolkienistic fantasy and less 4e/5e markings such as dragonborn, or other races making such appearances. Perhaps something more somber in presentation, though humor would still be there. More of a movie that has Ironman, Avengers or Captain America type promotions and writing rather than something that it turned out like (GotG, Antman, or Thor-Ragnorak type writing).