I'm not a gunsmith by any stretch of the imagination, but I'll speculate on your question.
The vast majority of .45 pistols I've seen on the line are built on the 1911 platform. I think the original reason for this was the availability of parts (being a military issue pistol) and the ability to custom-fit the barrel/bushing combination for maximum accuracy. The reason it's remained the platform of choice - it may just come down to the fact that it works, and no one has come up with a more popular solution.
There are a number of smiths building bullseye pistols with the Beretta 92 now and achieving exceptional results with them. That's good for centerfire and EIC matches, and a number of shooters I know have switched over. But, if you're going to shoot outdoor 2700 matches, you have to shoot the .45 anyway.