Why it is believable when circuit court nominees have waited through years of filibusters and brutal hearings for a chance for a job on the circuit courts? If one can go through that, I see no reason why the same judges wouldn't go through a brutal hearing for a job on the highest court.
The stakes are many, many times higher for the Sup. Ct. than for the lower court levels.
It's not so much that the hearings themselves are so brutal (although they became so for Thomas)- it's that the entire nationwide left-wing wacko character assassination slime machine (which includes, but is not limited to, the MSM) focuses all of its vast resources on destroying this one person. That simply doesn't happen in the case of lower court confirmations.