Why were the Capitol Police so woefully unprepared?
I don't buy into all the conspiracy theories suggesting that this was all a staged event intended to make Trump look bad. That may have been the motivation for a lot of the mutants who showed up to riot, but I don't think any government officials really had any part in that.
The simplest explanation is this:
The Capitol Police were unprepared for this because they knew damn well that a crowd of Trump supporters -- whether it's 5,000 people, 50,000 people or 5 million people -- are generally the most peaceful, normal human beings you'll ever meet.
Police showing people where to go
Capitol police escort them out