This is due to have the AID feature is designed. As I understand it after the 3 priority buildings: shrine, oasis, tiger dens(don't ask me why????) it chooses 50:50 between polish and motivate. Since most players only have a handful of cultural buildings, even if cultural buildings are prioritized regardless of age over decos, it doesn't take long before the cultural buildings are all done. Hence after the 50:50 split if polish is picked the game is left polishing decos no matter the age.its even funnier when the 4 or 5 popup messages say decs have been polished....even though we keep getting told they arent a priority
A simple solution would be a sliding bar for players to choose the % chance of polish vs motivate. Far from perfect as supplies would still end up not getting motivated a whole lot due to normally having a lot more houses than supply buildings.