Because let's face it, it's not worth $100 or whatever when you can get a whole bunch of other better games for the same money.
But then I see that picture that Tatsujin keeps waving around and I think to myself "I have 4 out of the 5 games for the Super Grafx".  I'm 80% of the way there.  Just one more game (and 2 cases).  But while I've seen the other 4 - and indeed bought them at - lower than average price, I've only seen one low priced 1941 that someone else had already bought.
So one way to get a copy might be to keep buying up duplicate games for cheap, and then trade with someone on here with someone.  anyone with an unwanted copy of 1941 and a shopping list of other stuff they want?