Justice Thomas should be the Chief Justice, but GW Bush was a racist coward.
He could have easily made Scalia chief justice.
To be fair though, its extremely rare that Presidents elevate a sitting Associate Justice to Chief, apparently because it rubs their colleagues the wrong way and "upsets the balence of the court" when a younger less experience justice gets elevated over a more senior SCOTUS justice. Rehnquist was obviously an exception to the "Presidents don't elevate sitting SCOTUS judges" rule, as was Harlan F. Stone. LBJ tried and failed miserably to elevate associate justice Abe Fortas to CJ in an 11th hour power grab before Nixon was sworn in.
Anyhoo, If Bush had stuck with his original plan of putting Roberts in as O'Connor's replacement, there wouldn't have been much ideological shift at all, and its possible Roberts wouldn't have drifted as left as he is now due to his status as CJ (if Roberts had remained as "conservative" as he was in 2005, he would have been a major upgrade from O'Connor)
Putting Roberts in as CJ was a big blunder on Bush's part, though I think Trump's SCOTUS nominees are even bigger blunder. I think most FReepers now accept that instead of "cementing a conservative majority" we only have TWO solid conservatives on SCOTUS, although its too early to tell if Barrett will step up (so far she's been a disappointment)
>>> GW Bush was a racist coward<<<
Not sure I would go along with the racist part.