There are some really ancient NC (or CNC if they actually had a microprocessor) machinetools from the early-mid '70's that were built on cards like that. Way before my time so I've only seen pictures on other forums, but each card would serve a specific purpose, like a linear interpolator or a resolver counter or whatever, and the machine would have a whole cabinet full of them on a wirewrapped backplane.
Apparently there are some of these dinosaurs out there still running too, which if those sold for real money, might explain why.
So that's my guess.