"Why did Springfield equip their Saint Victor rifles with Radian Raptor charging handles?"
Because they are darn good charging handles?
I only have one AR-style rifle (Ruger AR-556) when it cost a mere $499 on sale. After Ruger fixed some structure issues with the new rifle, it has run flawlessly, with a Radian Raptor handle and Radian BCG. I'm no expert, but it just works.