From my days in Marketo's support team I very often had to test things out for customers the end result being that found myself susbscribed to emails/newsletters. I continue to get some from time to time and I notice that it's very common for customers to stick with the default out of the box unsubscribe page and form.
If you haven't ever looked at your unsubscribe page please do, you'll find the default one in the design studio, if you do nothing with it then it will look something like this:
- I know, not very pretty, right? When I land on a page like this it doesn't leave a great impression, visually it's not good and also in most cases people are doing nothing to persuade me to change my mind and not opt out.
So please take a few moments to look at this, swap out the standard default grey template for one of your own custom templates, add in your logo, add in some rich texts to let me know what I'm loosing out on by unsubscribing, consider going the whole hog and implementing a subscription centre approach, here's an old Marketo blog that might give you some ideas.
A Community resource
A blog from Ed Masson