The unused material would probably expose the film’s rushed development and lack of direction. Things like Rey’s lineage were aparently still weaving around while filming had already started, so I’m sure other major plot points also shifted and changed all the way till the end of production.
While that is a possibility, I do think it’s in part on what the director cares to share with the audience. The deleted scenes that would’ve been shared would probably be too unfinished that even the normal audience would be lost. I highly doubt that it is because it would expose the lack of direction because u have rogue one which had major production issues and had no deleted scenes. Then look at solo, probably the most disastrous production of the Disney Star Wars movies, and there’s a bunch of deleted scenes. Even TfA, the original Blu-ray release didn’t have deleted scenes, only the second re release. I just think to quickly assume based on fan reaction and fan sentiment that that’s the main reason TROS lacks deleted scenes is premature