The toolmaker is just required to make the part..
that might have been the case when designers had the actual machining experience, and still some things would go back to be redesigned after prototypes are made, not the case these days, someone designs some weird thing because he has learned how to CAD, then a drawing is made and that gets sent around job shops for quotes, I often have to educate people asking/sending parts to be anodized about the problem of blind holes they make in parts, about 80% of time it turns out they could be made through, and avoid possible rinsing problems, cross contamination of tanks and cosmetic dye defects when the acid leaches out and eats the dye next to the hole, they just didn't know the problem existed...
and you wonder why you lose machining jobs to China? maybe that is a 5$ part made in thousands that now with that special feature get quoted by machinist shop for 35$, because the quote has to include the special tooling, high probability of broken taps, associated time trying to solve that issue and so on, just because the managers at either side don't want to do their job and manage things, they just push the PO order and evaluate the quote, then decide - with this lead time we can just order them from China at 20% cost...
I agree that if this was standard practice, everyone would argue how to make something and nothing would get done, but this doesn't seem to be the case here, if feature like this was standard, there would be tooling for it, I actually have around 100mm long M5 and M6 taps that might work here (that were not designed to do things like discussed here, just that the length might allow it to be done), but I would still ask the customer to see the assembly and then, if I indeed see some moronic reason for this 10xD continuous thread, I would raise an issue, with solutions mind you!
the problem with tapping such long threads is that spirals might not do it, the chip will probably break and cause problems when trying to reverse out, pecking such a long thread might cause it to be oversize at entry, through hole taps may work, but then the hole is very long, and chips might pack up and cause tool breakage again