A lot of these will be people who are looking for a way to make money easily. They have seen that you are successful and sign up, then realise they need to put in a lot of work to achieve the same results.
This is a bit of a generalisation but there are a lot of people out there weighing up the best money-making methods. They subscribe to numerous newsletters, putting them all into one shopping cart so to speak, and then remove those that aren't going to be the right path. In the end, they weren't invested in the path of writing, or in you.
I was taught to be grateful to those who do unsubscribe since I would rather have an email list of dedicated followers than people who aren't really interested in what I have to say - better open rates and all that!
Oh, and thanks for all you do, Zulie! I do enjoy reading your emails :)