Trade can be as short term as aid is; demand is very cyclical so if a country specializes in providing that good or service it can soon find that the product they are providing is no longer desired by consumers, or that there is a new product that makes what they provide obsolete. Even if there is a long term partnership between two trading partners it may simply mean tying the poor country into a different kind of dependency. Instead of the poor country being dependent upon handouts it is dependent upon the richer country buying its products or not trying to undercut it.