I think part of it is Maniac Mansion doesn’t give the impression of having an art style to begin with. Obviously it does, every pixel placed is a deliberate choice, but it’s definitely pushing less deliberate purely stylistic choices than Monkey Island 1 or 2 did. There was more space available from MM to DOTT to establish a style at all, while I think MI1 and 2 had a very deliberate style that they had to choose to move away from with Curse.
I voted for MI2, but love MI1 as well, and find Curse to be a visual/tonal delight that I just like hanging out in.