Trade can mean a great many things and so can war.
Sitting at the mouth of the Rhoyne and building ships so other men may journey far is trade, as is fostering a holding in what would become Qohor that sends lumber down the river to be milled and fashioned into ships. Or having a single tiny holding in a volcanic hell and making valyrian steel blades and armor and tools, selling individual models sometimes years apart but at a price that would beggar a fleet. Or being an artisan of blood magic, a flesh crafter, willing to perform... favors... for an appropriate degree of notice. Or being on board with other people's ventures and vendettas, Freehold or abroad, burning and bleeding for coin or opportunity.
Valyria would have been terrifying even if dragons had never existed and all a trader needs is to provide what others lack. Due to lack of opportunity, lack of interest or because they have their own calling that requires all their time and effort, because it is dangerous or unseemly.