I think the real question is why so many people praised him in the beginning?
I think that was really just because he wasn't an obvious crazy, like many of the people in Trumpty's administration. He was originally appointed to Homeland Security. I felt he was too zealous there. Sure, deporting people was part of his job, but it seemed to me he enjoyed it too much, and was more draconian than he needed to be.
But when he moved to the White House, he appeared to get off on the right foot. He fired the Mooch. He forced Bannon out. Those were good moves. He gave a press briefing in which he came off as being at ease, mildly humorous, and organized. He looked appalled when Trump made his "good people on both sides" comment about Charlottesville.
So far, so good. But it's been all downhill from there.