Why not go full Dura-ace front and rear?
Money, I found a random “salvage” DA caliper on eBay, and that was still like $100, which felt like an incredible score at the time.
The other thing is that one of my XG calipers started leaking, which is why I needed to replace it in the first place
Now that I have a setup that’s super light, works well, and is reasonably aero, I can’t be arsed to troll eBay for another deal, and then fork over another $100 for a DA caliper that may or may not work.