As a machinist I can tell you it probably has more to do with value earned for risk taken. Why should they take on the risk of working on your bow and maybe ruining it for a small amount of profit when compared to building bows from scratch. If you don't like the outcome, they have to stand behind what they do. The risk is to high for the profit earned. There are better things to work on from a business sense than to add bow bolts to peoples bows. That is why you find very few people willing to take this task on. You have to take on a lot of risk for a small amount of profit. It doesn't make good sense from a business model. Black Widow can keep busy and turn better profit without risking the outcome of a lost bow that you would demand they replace if it didn't come out right. I don't blame them for staying away.
By the way, you didn't say what you would be willing to pay to have this option added to your bow. It is a $200 option on most bows when it is being put in right from the start. What do you think might be a reasonable price for someone to take on the risk of ruining your bow?
Also, you will find that most bowyers are now using phenolic, micarta or stronger materials in their handles that they plan to use the bow bolt system on. This can't be accomplished on an already manufactured handle. The last time I talked about ordering a bow bolt with a well known bowyer, he would only add the bow bolt if the handle material was micarta. He had to much trouble with bow handles that weren't specifically strengthened for adding this option. Just some food for thought. jwingman