Long-term influencer partnerships help the influencer’s audience become accustomed to your brand, which increases their trust in you. In contrast, one-off partnerships are seen as more transactional and less authentic.
In some cases, brands add influencers to their board of advisors or leadership teams by paying them a salary or giving them equity. These influencers actively shape the brand’s strategy in the long term.
A few interesting reads about the subject are: