Most players grow up supporting another club. Some players drop this allegiance fairly quickly. Others might commit to a playing group (their mates) and love the coach and contribute positively on-field, but never change their traditional allegiance. Footy is a job.
Where this is the case, suggesting you need total buy in from every player to the entire organisation (ie they need to become an Essendon person) is misplaced. Rather they need to be committed to their footy team and playing with and for their team mates.
They don’t need to buy into the organisation-wide artefacts but they must buy into the team.