I don't know what they were thinking. Why duplicate such a popular cartridge? Instead, they should have come out with a single stack .45 ACP on a flatter full size frame (G17, G22, etc.) and I'm betting they couldn't make enough of them.
The G21 (which I've carried for about 15-16 years) was adapted from the 10mm G20. The huge frame was built around the 10mm cartridge, and simply converted to .45 ACP for the American market. It has a lot of empty space in the grip. If the G36 is a 6+1 gun, a full sized, single stack .45 ACP could easily be a 8+1 pistol.
But instead they come out with a remake of the .45 ACP cartridge? Remakes are seldom as good as the original. In this case, it wasn't even close -- as sales prove.