It's the same reason Warren Buffet, Bill Gates, Or one of the Walmart heirs would never run.

He's now far more powerful outside the white house than he could possibly be inside the whitehouse.

How could he have any less power than he has now?

There is a lot of truth to what you are saying.Public opinion of all politicians is now at a very low point --- the way we conduct elections and our government disfunctions makes it difficult to be an effective one (effective meaning something other than getting elected.)