Answer:
there's just a lot of drama around grumpy trumpy's StOlEN eLecTiOn which are all just fake claims. all his hardcore followers are brainwashed into believing anything he says, so people (especially people who are inside the capitol) fear that trump's followers might incite violence AGAIN even after they broke into the Capitol on the 6th.
That's why they have the National Guard and thousands of people to keep the building secure during Biden's Inauguration.
hope this helps!