We only had 4, they performed their roles really well, we raised a CN235 specific sqn too, I guess the small fleet was deemed too expensive in terms of overhaul and maintenance.
Can be many reasons.
We found cheap used C-130s from Aus and Belgium which increased fleet to 24 odd planes
CN-235 has narrow body, not much outsize cargo you can fit
As we bought many spare SAAB 2000s to support Erieye fleet, then CN-235 fleet redundent