I think he made most of these deals in the late 1980s and early 1990s (he wouldn't have been hard up for cash at the time, but the big checks for the film rights certainly would have been enticing). It was after the films started coming out that he took a hard line against film adaptations of his work.
He also now takes a position that the film adaptations damage his original work by changing them into a shape other than that which he intended, changes which become lodged in public perception. Some accuse him of hypocrisy on this since he freely appropriates other people's creations and reshapes it in his own work (such as in The League of Extraordinary Gentlemen
and Lost Girls