Blame it on the Republicans- yes Really.

First, Feinstein could step off the Judiciary committee and be replaced by another Democrat. But the Republicans won't allow a replacement so if she is off the committee it will grind to a halt any judicial appointments and block Biden from appointing people to the courts.

If the GOP wouldn't obstruct, I would bet money the Dems could get Feinstein to retire and have a replacement appointed by Gavin Newsome.

Adam Schiff would be a good replacement IMO but the primary hurdle right now is that committee assignment, not some conspiracy about whom to appoint.