Agreed. If the incumbent doesn't run (term limited or retires), the next nominee is almost always the VP if they want the job. Just look at the history:

  Roosevelt -> Truman
  (not Truman -> Barkley: the exception)
  Eisenhower -> Nixon
  Johnson -> Humphrey
  Nixon -> Ford
  Reagan -> Bush
  Clinton -> Gore
  (not Bush -> Cheney, who retired)
  (not Obama -> Biden, who temporarily retired)
  Biden -> Harris

I can't fathom how a party can pick a VP who isn't an excellent future candidate. JD Vance?