If you read enough marketing content, you learn an awful lot about customer loyalty.
Now let's think about your business. When is the most critical time-frame in the development of your customer?
You probably leverage a technique from fifty years ago or more, called a "Life Table" ... and you know that it is the twelve weeks after a first purchase.
In the month (0) of a first purchase, the customer has a 3.51% chance of purchasing again (in our example).
In the first full month after a first purchase, the customer has a 3.86% chance of purchasing again if the customer has not already purchased for a second time.
And then ... the slow descent into oblivion happens ... 2.41% / 1.92% / 1.63% / 1.43% / 1.08% and so on ... with a brief seasonal blip on month 12 (1.69%).
I cannot think of a project where this dynamic didn't happen ... sure, the dynamic is elastic ... better response for some clients and worse response for others.
And I've shared this fact with you pretty much every year for ten years. Your marketing programs should maximize a second purchase probability within the 0-12 weeks following a first purchase. This is where all of the magic should happen.
You - the marketer - can fix this problem, and in the process you might just overcome other challenges in your business. Fix it!