Because even when you and all the fellow members of your favorite Internet community decide to rise up as one and gather signatures and say "our voices must be heard! We will buy this game! You must localize it!", the chances are you could multiply your numbers a few times over and you would still be well, well below what a game like that would need to sell in order to be worthwhile. And that assumes that every single one of those people goes out and buys a copy, and that's something you simply can't guarantee.
Just to give you an example, the member list for this forum is just over 344,000 users. That includes every username account to have ever registered here, past and present, banned, active and inactive. If every single username on that list went out and bought a copy of a given game, it would amount to worldwide sales best described as "meh." Depending on the game, 340,000 might be an utter disappointment or it might be mildly impressive, but you get the idea. For a Digimon game, 340,000 units worldwide would actually be pretty good, but that's a very hypothetical high note.
You dig? I'm sure there are "people" demanding a localization of Re: Digitize Decode, but it's not likely those people represent numbers great enough to provide incentive for the product to be produced. You're focused on the system and not the game and inaccurately assuming the former will lead to sales for the latter.