Those 4 original plants not only (almost constantly) bare a lot of fruit (that often went into the yoghurt), they also produced new plants through stolons. The plants more or less clone themselves through of-shoots. Stick those stolons in a new pot with some fresh earth and it starts rooting. After a couple of weeks you can cut the 'umbilical' and you have a new plant.
My 4 plants produced another 24 plants this way... Remarkably quick and easy. I have no use for so many plants so I already gave a lot away to neighbors in the street. Tough luck for the market but the strawberry is a real 'resource based economy' plant. Good things that are healthy should be free of charge.