The inconsistent display of the unsubscribe header in Gmail is multifaceted, driven by Gmail's algorithms, sender practices, and user behaviors. Key factors include sender reputation (influenced by engagement, authentication, list hygiene, and spam complaints), sending patterns (volume and consistency), and technical aspects like implementing List-Unsubscribe headers and DMARC. Gmail may prioritize its unsubscribe mechanism if reputation is poor or complaints are high. The display may also vary based on individual user behavior, UI differences, display bugs, if they are sending multiple emails to the same address, or Gmail's internal spam filtering systems. Successfully delivered email marketing campaigns will need to consider all of these factors.