And the Congress provides checks for the judges
If memory serves, I seem to recall that you're from the UK. If so, then perhaps you don't understand how the Constitution established our government. No one, including judges, is above checks and balances. Since judges are unelected (except in some states for state level courts) and serve for life, there has to be checks and balances for them, too. Otherwise, they can easily become tyrannical.
The central theme for the writers of the Constitution was that unchecked power can not be allowed if we want to protect the freedom of everyone. Judges are no better than anyone else (and some have described them as "failed lawyers with political connections") and should be held accountable when they overstep their authority.