Most people who do not buy the first time would have bought later. They just never heard from you again. Following up is the cheapest revenue available to a small business, because the hard part, getting their attention, is already done.

Making it a routine rather than an intention is the whole point. It needs to happen in a busy week, which is exactly the week it stops happening otherwise.

You need two numbers, roughly: how many enquiries you get in a month, and how many of those you currently contact more than once.

If the honest answer to the second is almost none, that is the normal starting point, not a failing.