I think partly due to a management change, they suddenly realized that they were millions of dollars into funding a graphic adventure genre - a genre which is allegedly "dead" and "unsellable." Ignoring the fact (or disregarding its importance) that there are thousands of people with fond memories of the characters, and that Sam & Max themselves are a genre-defying set of characters if there ever was one.
Needless to say, they decided that it would be a smaller loss to cancel the game when they did rather than invest hundreds of thousands in marketing and getting the game in stores only to have it flop. It was a decision made out of fear, but on the other hand, in a big corporation it's probably the job of the people with the money to fear everything.
I think most of us disagree with their assessment of the situation, but in reality, will any of us really know for sure?