I mentioned yesterday that I had stumbled upon some .45 ACP brass that took the small pistol primer. As we all know, the Sainted John Moses Browning decreed that the .45 ACP be manufactured with large primers and till recently, that was the case. All .45 ACP took the large pistol primer.
Sometime in the recent past, handloaders started noticing that some brass, notably Winchester NT and CCI Blaser Brass were using small pistol primers. This thread over at the 1911 forum from 2010 talks about finding them, so small primers in .45 is at least three years old. It seems recently that Federal Champion ammo is now using the small primer in the .45 load. I understand that these primers are loaded in "lead-free" ammo ammo, specifically that the primers themselves are lead free.
The more universally understood reason is that it's part and parcel of a huge conspiracy to confuse and demoralize handloaders. The companies don't understand how resourceful, creative, and motivated we are, and the work-around is simple. Simply save your small primer brass till you have enough to load a batch, and load it for use where picking up brass is problematic. I'm saving mine till I get several hundred. We've learned that the fast powders used in .45 ACP fire up nicely with small pistol primers, so that's not a problem. The ammo goes bang.
However, it is a huge pain to sort brass based on the size of the primer pocket.