Butchers, like every other worker who uses a tool, are concerned with performance over time.
If any of the highly touted "super blades " allowed a butcher, or taxidermist, or skinner, to cut longer and quicker than another who used an easy to sharpen blade, then they would.
But all knives get dull and need sharpening and it matters little if they hold an edge twice as long if they take three times as long to sharpen !
Well, I guess since you've polled every butcher, taxidermist, and skinner on the planet, know what all of them universally use, and thus speak from authority on the topic, then you're more qualified to comment than me.
People of all walks of life use a lot of things for a lot of reasons, many of which have nothing to do with what is truly "best" in any specific single criteria. Perhaps a lot of butchers, taxidermists, skinners, et al have determined that a commercial knife is the perfect tool for them because they get performance they deem acceptable without the worry of beating up an expensive custom knife. As stated earlier, ultimate edge performance is but one of many reasons to buy a custom knife. The main reason for buying anything custom, regardless of what it is, is getting the exact design that you want rather than having those decisions made by someone else. To many, myself included, that reason, and the pride of ownership of having something nicely made and unique, is reason enough even if edge performance was equal to a commercial knife. You may think it's a waste of money, and that is valid as it pertains your wallet, but the OP asked for compelling reasons to buy a custom knife, and equally valid reasons were provided.
