How come it's rare for a great player to come off the bench towards the end of his career and becoming a role player?

I’m talking about the greats like Michael Jordan. How come he didn’t linger on and just be a bench player much like Grant Hill or Juwan Howard.

I’d imagine if Kobe played until he’s 45! Of course he’d be coming off the bench but couldn’t he be a dominant role player? A 6th man or just a 5 minute every other quarter kind of guy?

We saw Emmit Smith keep grinding with the Cardinals, what other examples could you come up with?