My guess is he wanted more money and creative control. Worst case scenario would be him wanting Snyder back as a director. His manager is The Rock's manager and she is probably hard to deal with as well. Henry Cavill is a solid actor but he needs to face the facts. He isn't a box office draw, he doesn't deserve A list money and his bigger role outside of Superman was MI:Fallout and his character is dead already. If that Netflix series flops, he's going to lose even more leverage.