While I admire the quality of the lens I can scarcely imagine a full time pro wanting to buy one. Manual focus for what is a portrait lens seems to be a recipe for frustration.
I'd only get one if I were a full-time professional and using a Nikon D810.
The other reason a pro would not buy it is because $4500 is a lot of working capital tied up in a tool that no client will appreciate.
Yeah it does seem like a poor business decision. I guess you could make that money back if you're one of the top pros earning thousands per job. For the average working person it's like 2 months salary for almost no gain in extra clients or work. Don't forget you have to insure that bad boy too!
I have a feeling Sigma are going to bring out an updated Art version of theirs soon at a quarter of the price and 99% of the IQ. The current one gets the job done as it is for most folk looking for an affordable 85.