While the logistical reasons that various transportation methods exist can be a fascinating topic for some, I don't think either of you is going to convince the other if you haven't already.
Given the economically-driven motivations I've noted so far, I'm surprised that one reason I haven't heard yet in the circle-networks-would-not-exist camp is that wizards get to charge for each use of teleport individually, over and over - so only a wizard driven by non-economic reasons would ever set up a permanent, "free" service instead.
Merchant: I'll give you a million gold pieces to set up a permanent gate!
Wizard: And destroy the monopoly that I and my guild-brothers have held over your heads for centuries? I think not.
Especially given any wizard who can cast teleport but not teleport circle can probably also cast dispel magic... at range. If people are desperate for teleport (having dismantled the infrastructure to trade in other ways) they suddenly are reliant on people who can teleport.At 11th level there is teleport trap which can allow really easy pirating of 'caravans' and can be made permanent.