This tradition started hundreds of years ago and you'll still see mention of it or illustrations in old story books and in art work from the past.
It was a way to bring other items for sale to the smaller towns and also for the farmers and other handicrafters to be able to sell what they had made.
For me? It was a way to get the very freshest fruits and vegetables to eat.
This particular market was on the road between where I lived and the US Army Post where I worked. It was only about a mile from my rental house. This particular day was a rainy day.
There will be several people selling fruits and vegetables and often they do not have the same thing-- and sometimes the crowd will be very thick in front of a particular seller's space and that always made me stop and look to see what "I" might also need to notice that they were selling.