Other mistake: At the beginning of the movie, when Roger is begging the director to give him another chance and keeps grabbing the bottom of the director's jacket that is in the director's hand, at one point the bottom of the jacket leaps into Roger's hand before he actually grabs it. (00:05:05)
Other mistake: When Eddie Valiant gets thrown out of the Ink and Paint Club, he is already starting to go through the air as the gorilla moves his hands to throw him. (00:21:20)
Other mistake: Three shots after Eddie stuffs the soap into Smart Guy's mouth, when the other four weasels notice him tumbling down the stairs, a chair can be seen flying across the room. This is impossible, because the other four weasels are together, and Smart Guy was talking with Eddie, so there was nobody to throw the chair. (00:42:15)
Answer: Maroon was simply greedy and Cloverleaf offered him a lot of money to sell, provided Acme sold his part too. Spoiler alert: Maroon was only trying to frame Acme (with the Jessica Rabbit patty-cake pictures), not kill him. However, Judge Doom turned out to be the owner of Cloverleaf and by buying out Maroon and Acme, he could get rid of Toontown (he hated toons). So Doom was willing to pay Maroon a lot of money (and when that didn't work, turned to murder).
Bishop73