If you were the person responsible for persuading airlines to come to SEN... how much more difficult would it be if you had to admit in summer 2022 post-Covid, you had ZERO commercial scheduled passenger flights ? Having a little bit of scheduled passenger ops also preserves organisational memory, competence and external credibility of being able to service 150+ pax jets and thus scaling up ops is perceived as realistic rather than a start-from-scratch job
While Easyjet flies a bit... Southend remains "in the game" and airline network managers may be willing to listen to a sales pitch. Without Easyjet, Southend would be at risk of being perceived by passenger airlines as suitable only for props, or be seen as sufficiently desperate that it could be asked to pay a very large marketing fee.