A common mistake people make is that they think that getting something means they will have it forever. Even if they don’t take care of it. Your car won’t survive it, your marriage won’t survive it, so why do you think you customers will?
Getting a new customer costs you a lot of money, time and effort. And giving good service is awesome but it’s not enough. You have to give your customer a reason to come back. Shay Carl said one on the Tim Ferriss show, that you have to keep up the courtship long after you get married. You do so much for your girl, you take her out, buy her flowers. All that work so she will have sex with you, why stop after you get married?
Start having special promotions for your returning customers. It could be special products or sales for customers who have been with you for a certain amount of time or that spend a certain amount on your services annually. If new people like to join in they can become customers too, they will get something similar but get them used to the fact that you value you returning customers. Soon they will become returning customers too.