You don't have to like it but you should understand that when IDPA was organized, maximum ten round magazines were the LAW, under AWB 1994-2004. There was a lot of hanky panky with magazines in USPSA, to the point I was surprised that the feds did not run a sting on the magazine parts racket.
Yes, I was alive then and was subject to those same laws spawned by the Omnibus Crime Act of 1994. The laws in most states didn't affect existing magazines, though, and there were a lot of them. I never violated those laws and I was able to acquire (legally) sufficient magazines holding more than ten rounds. I'll admit that my AR mags were in sad shape when I got them, but they functioned until sanity returned after those aspects of the law expired. I'm still using some of the Sig mags from those days.
Even if you think it was a reasonable idea back then, unless you live in a non-free state, what sense does it make now? Yeah, they finally allow 15 rounds in SSP, but the ten round limit still is in effect for ESP and the newish carry optics division.
Ultimately, though, I was talking about why I, rhino, don't prefer shooting IDPA when I have other options. The magazine capacity was just one element. The holster position thing was a bigger problem for me and you can't blame that on any laws.