Because it is a 16-bit application that won't run on 64-bit OS.

We cannot add a game knowing it won't run for a large group of our users, even to extras.

Basically, yes.

Here are my two credits.

The vast majority of Windows systems nowadays, even if you take XP into account, are 64-bit. For every user who could enjoy the Win3x version, there will be four who wouldn't. Since my department would have to deal with disappointed/angry users claiming that they only bought the game to get this particular version, I personally do not like the math here, regardless of whether or not we put it in extras, and slap disclaimers all over the product page.

This is kind of similar to our global availability rule. Either we sell a game that is available worldwide, or we don't sell it at all. Until such a day comes that we can release Win3x games on all modern Windows systems, the massive cons far outweigh the pros.