Why was this movie trying to be overly funny compared to the others?

IMO, Joe Pesci.

He was a hot commodity at the time this was made, his comedy skills were well known so they tried (and failed) to leverage those skills to benefit this movie. Unfortunately I think Pesci was at an 11 and they needed him at more of a 4 or so.

Overall this is probably my least favorite of the movies.

The second movie was already more comedic than the first one in the same way that Evil Dead 2 was more of a comedy than The Evil Dead. Look at how silly the third movie of that franchise was!

Back to LW 3, it's weird that they put Joe Pesci on the poster when he actually has less involvement than he had in the previous movie. It would have made more sense to have him on the poster for that one, and then put Rene Russo on the poster for this one.