I kinda think it’s mainly an issue with the Emperor. As Luke points out, the Emperor’s overconfidence is his weakness. Plus, he failed to sense Luke was on Endor too. The old man was just waning from old age combined with his complacent view of his Empire that was falling apart.
Or, buy my conspriacy theory that the old coot was digging his own grave: Emperor, Endor, Ewoks. EEE. Triple E = 666 in Star Wars confirmed!