Hell, one interview he compared seeing Star Wars for the first time as better than having sex for the first time!
I'm not discounting the nerd/fan angle either. Don't assume that.
I'm just saying that if the money is good, they'd do it.
If they love whatever the subject is and the pay wasn't good, they'd probably still do it.
Bpth are solid and logical motivators, but I'd probably assume the former as the first motivator just by reflex if I don't know the performer's personal life.
Vin Diesel is a D&D fan, even has his character's name tattooed on him. If they offered him a shot to star in a good D&D film I know he'd say hell yes.
Even so, if I didn't know this about him I'd still suspect they paid him well enough to keep him on camera.
You can love something and still be motivated by pay, plus you can forgo said big dollars if a project means something near and dear to you.
Even so, cameos and small inserts into films don't really equate to where I was going when you are the featured person in a show.