Yes it would cost ZCO more money to re-engineer the optical design of a current model in order to allow it to focus down to 10 yards. There’s no free lunch, they can’t just put a new knob on it with more numbers. The internals would need to allow for enough movement to get the full parallax range. That could mean redoing the optical prescription and or mechanical components. Regarding any difference in performance and image quality between these hypothetical versions, with good enough engineering you’re probably not going to be able to tell the difference.
I certainly can’t speak for the design requirements set by manufacturers but I speculate that part of it is simply institutional inertia and a little bit just not caring about a small niche of non-centerfire shooters.