The bad results obtained by Ittihad FC in several matches could be the cause although other factors might also be a consideration for the club to change coach. At the start of the season, there was news that Nuno Santos did not like the club's decision to buy an old player like Benzema, and rumors were increasingly growing that stated that Benzema has asked his agent to look for another club in the Saudi Pro League, although this was immediately denied by the club.
It's quite reasonable why Nuno Santoz doesn't like old players, because a good team must of course be built with young players so that when they find cooperation the results will last longer, unlike old players who may only last 2-3 seasons and then have to return looking for a replacement, but of course the club had other considerations as to why they chose to bring in Benzema, but indeed Ittihad experienced quite a real decline so changing the coach might bring about better changes, although it does not rule out the possibility of the same results this season.