Some like the chance to greet their fans, some are genuine introverts and all their skill comes out on the stage/pitch. Some are very socially awkward people who happen to be talented in their profession, but aren’t very good at meeting new people. Some love the limelight, others hate it...
Entitlement. I work in theatre and witness stage door twattery nightly. Many feel they are owed an autograph/selfie as part of their ticket price.
So if an actor uses an another exit, has to rush for their train, is meeting a partner, has their kids around, has a migraine, hates the general...