Many years ago, during an analysis of a proposed merger, I had the opportunity to analyze subscription behavior in a company who had switched all of their annual subscribers to monthly charges.
Over the course of 3 months, 70% of subscribers cancelled their subscriptions within 30 days, and 100% had cancelled within 3 months.
While this was a complete shock to me, it avoided a disastrous mistake by the company I was working for. We kept annual subscriptions, with notification far in advance of renewals.
I always consider making a contribution to devopers whose work I enjoy. I will NEVER, however, sign up for a monthly fee. Please change your policy and allow those of us who wish to support your developers on our own terms contribute.