To throw in my two-cents here, most of the carbon steels are fairly easy to heat treat but not in batches. I get the best results when I handle them one at a time which commercial processors don't like to do. Also, some steels quench in oil, some in water, and some require the quenchant to be at a specific temperature so it's not easy for a commercial processor to be set up for all the possibilities especially when most knifemakers do it themselves.

Further, you get the best performance from a carbon blade when you either edge quench it or draw the temper on the back of the blade. That's a one blade at a time deal too...