This is probably because you may not be working tirelessly to convince your clients that your product is the best solution for their needs. Try to build a line of communication that enables them to see that you're not just after their money, but you're genuinely interested to know how you can better provide for their needs.
This line of communication opens doors to aspects of their needs you may not have even thought of. It's also great because it gives you time to fine-tune how your product provides the best value to them.
By having a good relationship with potential customers you are able to let know about the amazing new products and services coming up in the future, as well as any new developments you've come up with, instead of diving straight into a sales pitch at each juncture.
You get to build a rapport with them. This gives you a great advantage because if this particular customer ends up not needing your product, they'll definitely have contacts that do and just like that you'll be able to get a new customer and a higher chance of sale.
Building relationships isn't going to take a day, it can span over weeks and even months. Be patient and understand the core of retaining customers – understanding their needs and providing the solution for it.
Opens a line of communication
Gives insights to customer needs you may not have thought of
Shows customers your development
Opens up room for recommendation