Well, I suppose it's moderately better than having your former benchmates investigate?
Like I said, they are going with the friendliest "impartial" court to provide cover, because without doing anything the legitimacy of the highest court is in question. Assuming Kavanaugh is cleared, that may also mean he no longer has to recuse himself from cases brought by liberals.
Article summarizes how it ended up with Roberts:
These complaints were initially received by the U.S. Court of Appeals prior to Kavanaugh’s seating on the Supreme Court. Chief Judge Merrick Garland — whose nomination to the Supreme Court was blocked by Senate Republicans—recused himself from the matter. The complaints were then passed to Judge Karen LeCraft Henderson, whom President George H.W. Bush nominated to the bench.
Judge Henderson dismissed some of the complaints made against Judge Kavanaugh as frivolous. But she concluded that more than a dozen complaints were substantive enough to warrant investigation by an impartial panel and that they should not be handled by Judge Kavanaugh’s fellow judges in the D.C. Circuit. She referred them to Chief Justice Roberts, who has now referred them to the 10th Circuit.