That's a different problem, there are apparently hundreds of them and I'd wager that a significant chunk of them are dressed up like they are eberron's dragonmarked houses but larger or the east india trade company; but the world shows no evidence of such a power & they certainly don't act like a power of that scale when robbed of their very FR specific plot armor. They don't act like mercantile companies, grow, wield their power against the nobles/ruling body, join & consume each other, or any of the other things such a organization does. Because everything else is an empty shell of plot armor they don't have any logical structure. There aren't even any nations in the world for them to operate within/between but instead of building corporatocracies or something you have these plot armor castle towns pretending to be megacities that wield tremendous clout yet are somehow able to function despite a level of infrastructure & management of the surrounding area that makes the darkest corner of the dark ages seem positively well oiled. The overuse of plot armor protected loose threads that go nowhere & creation of hollow do nothing groups to provide continuity porn means that players & GM's can't simply infer how the world will react to an action simply by thinking as a human player/gm in terms of most authors are human.There certainly are merchant costers in FR, they are outlined in the 2E campaign set, and there is mention of trade goods in the 3e campaign setting. And if Im not mistaken there are trade routes mentioned in various other supplements, for example, the 2E city of splendors. But that would be a cool 5E supplement, one that has never been done is a book on merchant costers, trade routes and goods in the Realms all in one book.
Someone brought up fixing these kind of problems would require deciding if x or Y event happened & shaping things from there, but that's absurd because it's not like FR has some deeply respected continuity bible like a lot of tv shows/comic books/etc have. The past shapes the present yes, but you can't view the present by looking at all possible pasts and refusing to condense them into a present with bones made of something other than plot armor