How so?
Having Antonin Scalia, former Supreme Court Justice, advocating for your case in front of the Supreme Court brings all sorts of problems to mind. Sure, he could retire and do so now, but he'd be giving up tremendous power. If he was term-limited out, it'd all but guarantee that he'd be doing just that (along with every other Justice).
Double the size of the court, maybe. Then every individual judge isn't so important, so the fights over lifetime appointments to single spots aren't quite as drastic. As it is, I believe we have one of the smallest Supreme Courts in the western legal world.