Creating a private game servers is a way to learn both technical and soft skills you need to get a job in the future, it's in no way an easy task tho, so brace yourself.
Although they are usually called private game servers, those servers are open to the public and definitely want to get the most players as possible. People playing game servers are the customers. Important factor is also monetisation, which is done through Item Shop people can buy Premium Items and such on server site and then spend it or use them ingame. Usually some of these items are very hard or impossible to acquire only by playing game, which is kinda how those servers are kept online and operating.
You many not take those private game servers seriously, but keep in mind some of them have thousands of players joining every day and each of those players is potential customer.