of light airframe MIO and CAS

I've been wondering, why do nations who in vanilla relied on their light airframe MIO to produce CAS got this ability removed from them, especially when some paths of the MIO are geared toward ground use of planes (left one if I remember correctly) than air to air ? Is it intended to nerf some nations CAS, a decisions from the devs or just something forgot as a bug in the code ? (not sure about the tag though)

here's an example, R-5 CAS, who are in vanilla built by MIG are not assignable to any MIO