The point of an email list is to engage with the people on it, and to build a relationship with each person. Ultimately the point of the relationship is to make sales – either to the person on the list, or through them to people they know.
That said, if a person on your list is not engaging with you by at least opening your emails (hopefully reading the content and clicking on the links) at least some of the time, you’re wasting your effort and their time by continuing to email them. You should periodically “wash” your email list by attempting to re-engage with the individuals and, if that doesn’t work, removing them from your list. A small, dedicated and engaged audience is better than a larger audience that doesn’t give a damn about you.