#2 The writing was on the wall
Following his dismissal as Executive Director of RAW, Sean Ross Sapp of Fightful spoke to some Superstars backstage. Some of them were disappointed as Paul Heyman had given opportunities to younger Superstars, and most were surprised at WWE's announcement. Others backstage have reportedly said that the writing was on the wall with regards to Paul Heyman's removal as Executive Director.
We are not quite sure what they meant by this, but could it perhaps mean that there were some disagreements between Heyman and other people in power backstage?
Heyman and Vince McMahon have previously butted head, which led to his exit in 2006, and he's known to be a vocal figure, who has been steadfast and backed his ideas. There were some rumblings about a disagreement between Heyman and McMahon last year, as reported by Sportskeeda's Tom Colohue.
Heyman has been given a lot of creative freedom backstage, going by various reports, and this not resulting in good viewership could have resulted in WWE deciding to release him from his Executive Director position.