Stallonne made them an offer, they said fuck it.
Jean Claude Van Damme was at some unknown press conference here, doing a Q&A thing with the press and of course, somebody had to ask him why he turned down Stallone’s movie, “The Expendables”. Simply the reason, because Sly wouldn’t give details on the character Van Damme was supposed to play. Van Damme asked many times what the character is and Sly just kept saying it’s going to be a great action movie that will make him lots of money.
That's coming from someone who starred in Street Fighter The Movie.