The stories diverge from there and the reasons include: Van Damme was too short to play the Predator, he kept passing out due to the heat, Fox executives didn’t like the suit and Van Damme was collateral damage, he complained too often about the filming conditions and he shattered the $20,000 head for the costume.
Everyone is in agreement that Van Damme didn’t like the suit (a feeling shared by everyone else involved) and that he clashed with Joel Silver.
If one thing is clear about Van Damme’s firing, it’s that no one is clear about what happened.
All are really distinct, detailed reasons, so why no one is on the same page is a mystery in of itself.