The only conclusions that I would draw are that the data is incomplete, and the regulations have nothing to do with animal cruelty or wildlife management practices
Actually, a lot of the regs defining what is and isn't legal to use are based on animal cruelty concerns, game management practices and general hunter and public safety concerns.
Sometimes the reasons actually make sense, sometimes they don't but generally they are not well communicated to the public so we have a lot of regs that appear not to make sense, just because the reasoning behind them isn't or hasn't been well explained.
Also keep in mind that the regs are not about what can work, or what you or I the ethical guy would do, but are based on what they see and feel the majority of people hunting would do, absent specific regulations.
And that the regs to change some, with time, in some places. I have no data to back it up, but I'm sure that if you looked at the regs 40 years ago, you find just about the opposite with the .223 and deer. I think you'd find the majority of states prohibiting it and only a few allowing it.
40 years ago when I moved to WA their regs about pistols and deer were very specific. There were a few cartridges named as allowed, provided they were in guns with 6" or longer barrels and had expanding type bullets. There was also a minimum ft/lbs energy @ 100yds required. ,357 Mag just barely made it with some loads. 9mmLuger and .45acp were specifically excluded by name.
At the time, I had a nice, old model Ruger Blackhawk in .41 Mag. Met all the requirements, but one. Mine had a 4 5/8" barrel, not a 6", so wasn't legal for deer. I wound up trading it for a .30=30 Marlin...
which was legal for deer.
The idea given back then was, the regs were tight to prevent people from going after deer undergunned....
After a couple decades of actually looking at what people were doing and using, they realized that the majority of people were, if anything over gunned for deer hunting, due to the regs and their own choices.
So, after a while more, they changed the regs, dropping the energy requirement, and changing the min barrel length down to 4". And setting the bullet size and weight the same as for rifles, .240" or larger and 85gr or heavier.
Today, my old .41 Blackhawk would be perfectly legal for deer hunting. Pity its long gone...