My understanding of the reason for the long reach caliper on the back, and the short reach on the front, is because the front fork has a vertical drop out, so the relationship between the rim and the brake pad doesn’t change.
Whereas, the rear/back wheel, has an adjustable range, due to the semi horizontal drop out.
So the rear caliper needed a larger adjustment range for the rim/brake pad relationship.
Not sure, if this is actually the case, but that’s just how it was explained to me.