I think that he is a liar and those institutions, filled with humans as they are, also are undoubtedly staffed by people who are politically motivated liars (as is any institution that is staffed by human beings).It's incredible that you guys think all these other people and institutions are absolute liars, but Trump is as honest as the day is long. What world do you really live on?
That isn't to say that every member of those institutions is corrupt, or inept, or a liar, or someone motivated to use their power to hit political opponents but I think there are those elements in those institutions. Conservatives used to have a healthy distrust of government overreach, I think it is natural to question that if people in the Department of Education can have their own politically motivated intentions, why not also people in the DoD, CIA, FBI, NSA, etc.?
It has been my observation over the years that when government institutions "lose" things or are less than transparent, that often means they feel that knowledge in the hands of the public would make them look bad for some reason or another. So we do this dance where they conveniently lose a video of something they blamed on the right wing and went from "We can't talk about who and how many we had embedded in that crowd (if anyone at all)" to "of course we had people in the crowd but we can't tell you what they were doing...." And remember this is coming from a group who has shown itself to me more than happy to push people towards crimes, to the point of having more of their informants in a cell pushing for even bigger crimes, all in the name of getting a conviction (See Gretchen Whitmer "assassination plot").
All these conspiracy theories develop when government gives the appearance of hiding things or is flat out caught lying. Both of those elements exist around Trump. So no, it isn't really shocking to me that people don't take all these agencies at face value. There are very high profile instances of them having been caught flat out lying about things to either make Trump look bad or to cover for their favored candidate. Trust is earned. They burned bridges. I don't go as far as some of these other guys with my side eye, but I understand why they feel how they do.