I didn't know this until recently. They are appointed by the AG as they are employees of the DOJ, not federal judges in the judicial branch of the federal government. They can be fired at will, and the DOJ has mass fired immigration judges who do not bend to the MAGA agenda.
So Bondi can stack the immigration courts with MAGA loyalists with no Congressional oversight. It takes years to denaturalize naturalized citizens? No problem. Appoint a bunch of Proud Boys to preside over denaturalization cases. Done in a day.