The idea behind this was afaik that wheeler based vehicles take damage from barbed wire, treaded vehicles don't. The Reckoner being a halftrack, so kinda falls in between.
Ultimately it was a decision made for balance reasons, but I can't comment on the reasoning here as that was before my time. I think it was supposed to give the few vehicles in the early stage of Nod gameplay an edge to keep up with the GDI, which on the other hand have an additional RT sink.
Whether this is good or bad is ofc open for discussion.
