What value do you place on your time?
I recently resigned from an unpaid role managing a Facebook page for a writing group. I've been in the role for a year and I felt that the time had come to move on and use that time and effort more effectively for my writing career. That was the main reason.
The second reason was that during the past year, the 'founder' of the group has expected more and more of me and has been unpleasant, to say the least, when I have tried to discuss the page with her. My resignation was met with an outpouring of poison from this person.
One of the unfortunate factors of offering our time for free is that certain individuals will have no respect for our effort. If they are not paying us for time spent managing a Facebook page or in writing an unpaid article for their site, those individuals will treat us as if we are offering them a sub-standard product.
Do not accept such treatment. You know the true value of your time, effort and writing. Do not let such individuals disrespect you in this way.
There are plenty of individuals out there who will appreciate your free time and free articles and give you the credit you deserve. Work with these people. They are truly worth your time.