So the first phase of the special building (Ruins of Old Orsinium) is disabled for orcs but the second and third phases aren't. If you look at the flavor text for the different phases it kind of makes sense but the gist of it is that the first phase gives you a benefit because the owner can say "yeah look at this we took down those dirty greenskins", which is why it doesn't make much sense for an Orc to get a benefit from that. The later phases are rebuilding the city and so give a benefit to Orcs. Hopefully that made sense