As far as we can tell there are two sets of troops on the moon.

There is the detail sent to guard the deflector base and the hidden Legion sent to close the trap on the Rebels.

Remember at the beginning of the film how twitchy Jerjerrod is?

Remember his attempts to win Vader around with his pleading for more personnel?

The deflector base could be argued as being under his command.

It was probably built before anything else on the Death Star was.

What if his troops were being massacred down there but he has been covering it up so as to not get on the wrong side of his superiors.

We have already seen two films where that sort of failure doesn't end well for Imperial officers.

A good point of reference would be The Eagle.

Another would be the story that probably influenced Star Wars more than any other Dune.

The Ewoks could be like the Fremen, the high command of the Empire just think they harmless savages but they have already been kicking the crap out the Imperial presence on the planet.

Fear of being seen to have failed has created a cover up which would end in disaster for the Emperor's plans on the moon.

Just as the Jedi couldn't see their end until it was too late, Palpatine's hubris has tipped the balance of the Force in the opposite direction which would all pay off in the last act.