Several factors can contribute to user inactivity. One of the primary reasons is content irrelevance; if your emails are not providing value or are not aligned with the interests of your subscribers, they are likely to lose interest. Frequency is another factor; sending too many emails can overwhelm subscribers, leading them to disengage. Conversely, sending too few emails can make them forget about you. Additionally, poor email design and user experience, such as non-responsive layouts or confusing calls-to-action, can also contribute to inactivity.