Because the supposedly coequal branches of the Federal government have deferred to the courts for so long that they've forgotten how to read the plain meaning of the Constitution for themselves and, in the case of Congress, forgotten that judicial overreach can be understood to be a "high crime or misdemeanor" in the original meaning of the phrase. One impeachment of a judge for legislating from the bench would probably do the trick, but there is no desire to do that on the left since the Federal bench advances the left's agenda more reliably than elections do, and no will to do it on the right, either out of a misplaced conservative deference to precedent or the foolish desire to curry favor with the media and the Washington social circuit.
Only fifteen federal judges have ever been impeached, and the Senate has only voted to remove but 8.
In reading about them, it appears most are removed for kickbacks and the like rather than wrong usage of judicial power.
I would certainly like to see a federal judge who brazenly impugns the judiciary power removed from the bench. Until then, our best hope is to not let them onto the bench in the first place to cause havoc.