Marketplace
What brought most people to live in the towns was business, meaning trade and commerce. As trade grew, so did towns.
At the start of the middle ages, only luxury goods were sold and traded for, but eventually everyday goods were sold all over the markets in town, just like we have now.
The town markets were always busy with people buying and selling food and goods. Goods such as silk, cloth, glass, dishes, candles, and more were sold. In addition to that, foods (bread, animals, stew, veggies, spices, etc.), toys, and more were also sold!
Often times, towns would have large merchant fairs. They would "clean up" the town to prepare. These would attract all kids of merchants from all over the world. They would do this a couple of times a year. People would offer samples and sell their goods from afar to the people of the town.
With the growth of trade and commerce, merchants started to become very powerful and wealthy. The ran businesses and looked for trading opportunities or other business opportunities sometimes far out of town. Merchant guilds came to dominate the business of towns and cities. In towns that became independent, merchant guild-masters often sat on town councils or became mayor.