Originally posted by Kailas:

There is not enough resources on the map. Perhaps instead of making cities produce a base of 1 resource you reduce the overall income from trade so there can be more resources on the map yet less overall gold from it. At this point most of the game I am very hard pressed to get the resoruces I need to get the bonuses. Most of the ai countries do not get even 1 resource for import which is another issue perhaps caused by the lack of the resources available but I do remember even in vanilla AI didnt try to get max trade going