In most cases this is buyer turnover or, customer attrition as the correct term. There is a process of buyer churn which is the time period of the customer attrition as a group (the whole). Start with 100 customers, the next month you have 70 left, the next month 40 left, and so forth.

There are two solutions;
1. New Customers.
2. Customer retention efforts.

Specifically to cam sites: The buyers get the bill for their fun and in many cases the money spent is money impulsively spent -- They consciously decide to spend less.

With regard to the ''whale buyers'' they will burn-out for lots of reasons.

I have always seen the $50.00 to $100.00 /mo buyer as very average in the premium cam business. There are some that only buy once for $20 to $50 but I have seen customers maintain the $100.00 a month spending level for many months. Their "hobby" is camgirls