In modern times any street with so much foot traffic is lined with shops to take advantage of all the potential customers. Remember that when walking you have p

In modern times any street with so much foot traffic is lined with shops to take advantage of all the potential customers. Remember that when walking you have plenty of time to take in the shop window, and taking a quick detour into a shop or pub isn't much effort. Especially if traffic is moving slow anyways. It's not at all comparable to driving past in a car. I imagine the same reason made it attractive to have shops on one of the main streets into London, even if it happened to be a bridge. And once you are erecting a building for the shop or pub, why not add a couple stories to house the shop owner, workers, or anyone willing to pay rent for living inside the city wall?