Because ouch.
But I'm right there with you and would probably trade away mu XDs-45 in a heartbeat to pay for a 10mm version. I load my own, so I would reserve unpleasant nuclear loads for the woods, but keep them to 40 S&W velocities for urban environments.
Unfortunately I believe SA would sell about 7 of these, and 3 or 4 of them would be to people participating in this thread.
I agree.
Where I really think SA is missing the mark is they should have kept their 3.8" double stack XDm around, and put it in there. That would be direct competition to the G29, and since I dislike Glocks, I'd bite. It'd also be a lot more pleasant to shoot. As it is right now, I find my interest in the full size XDms in 10mm faded very fast.
What I REALLY think they should do is chamber an XDs for 38 super. You'd end up with a 7+1 fairly mild shooting pocket rocket, though recoil would still be substantial. Unfortunately it would be way too much of a gamble on SA's part, as reliability would be a problem as some shooters use Super Comp brass and others use rimmed, and decent factory SD ammo isn't exactly overwhelming store shelves. None the less, I'd buy one immediately if they ever did it.
Both of my Sig P220s in 10mm have been 100% reliable and are pretty pleasant shooters.
However, despite that, I still think Sig should have made an all steel version of the P227 in 10mm. I bet it would've outsold the P220 version since people like capacity. None the less, My P220s are keepers.