Conkers problem was two fold first was the issue of delay, and the second was of timing. The multiple delays frosted over interest, and when the game finally arrived the console was not long for this world. Most 64 owners by that point having already moved on to new platforms, and the sales trend of the consoles software due to lack of software had ebbed off.
Had the game arrived earlier in the consoles life it might have done surprisingly well. We will never know. Instead it exploded into a barren wasteland with hardly anyone there to pay attention. Followed by the debacle that was the Xbox release did not help the franchise either. I have little doubt retailers railed against the title for one reason. The game looked like a game for young children, but was adult oriented. So you have the Joe Camel stigma associated with it.
Personally I think the game was ahead of its time, and the concept will probably not be revisited for many years. Traditional platformers will still be dominated by shallow story, and little adult humor. Which is a shame every other genre has been given a chance to grow up, but not this genre. Had the profanity or the crude humor been in any other genre it would have gotten the green light.
I hope Rare does develop another Conker game down the line. Killing Frenchies was ever so much fun.