I'm not really the confrontational type that would normally say this but....
If you don't like it, don't buy it.
I don't like my sister-in-law's Scion XB, it's the ugliest car I've ever seen, tiny, and when you put your foot on the gas, it feels like it would accelerate faster if I got out and pushed. But she loves it, and I don't have to own it. Different strokes for different folks.
For what it's worth, it's a marketing thing. If you consider that the current majority demographic of handgun buyers are buying their first gun - or at least their first handgun - then it all starts to come together.
"Cool" sells, and "different is cool". Everybody and their dog has a 45colt revolver, but old cowboy guns just aren't "cool" to most younger folks these days. It's easy to sell something different. 45acp is different. Birdshead is different.
Different also sells to those of us that have a couple sets of 45colt revolvers in different flavors. I don't really have a use for ANY new revolver, but if they came out with a .480Ruger Vaquero, I'd own a pair. Just because they're different than anything else I have in the safe.
Why the .45 ACP? Why not .44 Special, .44 Russian, or .45 S&W? The .45 S&W would be the choice alternate, in my view ~ short cased, heavy bullet at moderate velocity.
Cartridges that are associated with black powder and lead bullets aren't as cool as they should be to new shooters. The only one on that list that you can find regularly would be the special, and even that is a crap shoot. If a shop sells ammo, they sell ACP, and they sell it cheap. Heck, it's often more expensive to get most of those on this list than WWB 44mag!
Also, I think it has to do with the fact that the good reputation of the 45colt has also been sullied over the years, as it's become viewed largely as 'left behind' by more powerful rounds, or viewed as "under powered unless you reload." Alternatively, the 45acp reputation is as strong as ever, bolstered by the current "prepping fad" and the whole "zombie apocalypse thing". So even though they're really about equivalent, the reputation to NON-gun folks is favorable for the 45acp, and disinterested in the 45colt.
And of course, ammo cost is a major driver for the new handgunner. 45acp ball ammo is about the 4th cheapest centerfire ammo on the market, and new handgun buyers do their research. New handgunners don't usually buy ammo online either, they buy a few boxes locally, so the selection and price plays into that.
So right, wrong, or indifferent, I can understand why there's such a draw for the 45acp Sheriff's model. I dig sheriff's models in all flavors. If all goes as planned, by the end of spring I'll have birdshead short barreled Ruger Vaqueros in 44magx2, 32H&R mag, and 45colt/45acp.