There was a great breakdown by a Villa fan on Reddit but I didn't save the post. Apart from the obviously terrible results (especially compared to what Emery did with the same players) he also possessed basically every negative trait a manager could have (at least for his Villa stint, I did not follow him in Scotland). Alienated dressing room leaders for no reason, didn't trust the youth, poor communication with the players, miserable touchline demeanour, hostile towards both fans and journalists, overall negative and pessimistic outlook. I remember he told the media before a game that Chelsea should be coming to Villa Park and wiping the floor with them, for example, which understandably grated the fans.

This was in addition to the on-pitch issues where he put forth puzzling selections, didn't have a clear gameplan, wasn't good at using subs and also couldn't adapt to individual games tactically neither before nor during matches.

This video explains a viewpoint on what's happening: https://www.youtube.com/watch?v=0F4yg2odqHg&pp=ygURc2F1ZGkgaGl0YyBzZXZlbnM%3D

I guess they want to make the Saudi league super known and famous, and buying big names is a great way to boost popularity.