Leslie Carbaga's excellent book on the Fleishers tells the whole story of the Fleischer's big move of their entire animation unit to Florida, and their subsequent ejection by Paramount.
Mr. Bug Goes to Town didn't destroy the animation pioneers' credit with Paramount, although it's often told that way, and this was Paramount's favorite version of the story. According to Carbaga, the big studio, more than anything, wanted to get their mitts on the animation studio and ease the famously bickering brothers out of the picture altogether. Mr. Bug provided them the pretext to do just that. --The sad closing of a great quirky, innovative chapter in American animation.
I wanted to comment, also, that the film actually debuted December 4, 1941, not December 7. That may have been close enough to do the trick, anyway, in terms of national mood damaging the film's success. But another part of the legend of this troubled little film is that it was killed by having the bad luck to be in the theaters at the same time Dumbo (released October 23, 1941) was still doing very brisk holiday business. I haven't done the research into box office numbers, but I'd say that Dumbo's concurrent presence in theaters likely had an impact on Mr. Bug. Movie-going was at an all time high at this period, and successful films could go strong in theaters for months. -- Something unimaginable in these typically short-run, quick to-DVD days.