"I saw you on CSpan!"
"I saw you on American Experience!"
It is nice, very nice, when people see your work and like it. Sometimes I watch, sometimes I don't. Often, I just don't have the opportunity to see it.
As many of my historian friends can attest, the pay for most documentaries is pretty small, if at all. So why do we do it? Because people come up and say, "I saw you...." and then maybe they buy your books, or support your cause, or just learned something over the course of an evening.