Why were Capitol National Guardsmen removed from their posts?

A Guardsman told Politico that once they were removed from the Capitol building, they were told to "set up mobile command centers outside or in nearby hotels."

National Guard troops are seen near the secured zone set up for the inauguration of Joe Biden as the 46th President of the United States, near Black Lives Matter Plaza, in Washington DC, US, January 20, 2021.  (photo credit: REUTERS/LEAH MILLIS)
National Guard troops are seen near the secured zone set up for the inauguration of Joe Biden as the 46th President of the United States, near Black Lives Matter Plaza, in Washington DC, US, January 20, 2021.
(photo credit: REUTERS/LEAH MILLIS)
After guarding the Capitol nonstop for close to two weeks since the January 6 insurrection, thousands of US National Guardsmen were told to take their 12-hour shift break in parking garages with few amenities and in freezing conditions, Politico exclusively reported on Thursday. 
Lawmakers from both ends of the political spectrum reacted quite strongly, and by nightfall, a Guard source confirmed to Politico that all the troops were ordered to return to the Capitol. 
A Guardsman told Politico that once they were removed from the Capitol building, they were told to "set up mobile command centers outside or in nearby hotels," while others packed into parking garages.
According to a different Guardsman, the parking garage he was ordered to provided only two bathroom stalls for 5,000 troops. There was no internet reception and one electrical outlet.  
Politico spoke to various Guardsmen, who maintained they were not told precisely why they were ordered to leave the buildings. 
If this is true, it's outrageous. I will get to the bottom of this," tweeted US Senate Majority Leader Chuck Schumer. 
Some 25,000 National Guardsmen were called up on the day of US President Joe Biden's inauguration. 
At the time that 20 National Guardsmen watched over a few protesters shouting anti-feminist and anti-gay chants. 
One day before the inauguration, two National Guardsmen were pulled from duty following a vetting process. They were found to have connections with extremists.  
Arkansas Republican Senator Tom Cotton responded as well, tweeting, "We’ll get to the bottom of this and get it fixed. Congress is in session, but buildings are still closed to public, so there’s plenty of room for troops to take a break in them."
When the January 6 riots occurred, and the Capitol had been breached, the entire DC National Guard was ready to provide backup if needed. 
Cotton added that, with the inauguration ceremony over, "We should start getting the Guardsmen back to their families, jobs, and communities anyway. The extreme security measures of the last couple weeks can be substantially reduced." 
Reuters contributed to this report.