Why aren't all the 12ga bores the same? Isn't there a preferred bore?

We had the big bore era. I have heard of 780 bored barrels. Perazzi has had 724. Why haven't we learned the best bore size? Or do we know?

 

Certainly not an expert on the matter, but the industry is not going to re-tool their individual manufacturing process to become uniform with everyone else.
I believe back boring was at the beginning of the experiment by aftermarket gunsmiths on target guns. The idea was to reduce recoil and produce more uniform patterns. When the gun makers realized the success they were having, they began to incorporate the process at the factory. The manufacturers kept going until the bores became so large they began to lose the gas seal.
I had a prominent person at Ljutic tell me that they wouldn't go any bigger than .730 because of this problem.
I think they have all pretty much settled around .725 to .730.
I'm sure there is enough data now days to know what the optimum would be. But its probably not necessary to be uniform because there's really nothing to gain.