Answer: by working with a publisher who would help the developer bring their games to stores and then market them and get as much exposure and traction as possible
Step-by-step explanation:
Publishers were and are still important in the gaming world even if they have now increasingly moved online. Publishers have a reputation and with this reputation comes access to a wide array of services that enable them to sell games.
This was the same when most stores were brick and mortar. One would sign a deal with a publisher who through their expertise would help the game get to market and give it publicity so that it can be sold.