There is no reason to have 25,000 troops in DC.
The reason was to secure the inauguration.
There was no credible evidence there was going to be violence on any scale (beyond the 'normal' violence we see in Democrat-run cities every day), let alone the scale that would require 25,000 troops to stop the violence.
Yes, there was. The Capital was attacked 2 weeks earlier, the goal was to stop the winner of the election from becoming president.
Some of the people arrested for storming the capital were planning more attacks (like the guy with the horns)
A bunch of different LE agencies said they were aware of multiple plans to attack the inauguration.
An FBI memo for example:
"The FBI received information about an identified armed group intending to travel to Washington, DC on 16 January. They have warned that if Congress attempts to remove POTUS via the 25th Amendment, a huge uprising will occur."
All major social media platforms reported users planning attacks.
let alone the scale that would require 25,000 troops to stop the violence.
The goal isn't to have enough troops to win a battle against domestic terrorists, it's to make the terrorists not even bother trying.
The US did not have this many troops guarding DC when it was at War, including during the Civil War.
And in 1814 there were only 5,500 American troops. And they burned down the capital. (I consider both our statements here irrelevant)
The presence of this many troops has nothing to do with the riots, it is a show of force on the part of Democrats.
It has to do with the threat of another terrorist attack. And yes, it was a show of force, to discourage anyone from even attempting to try something. But the troops were requested by the people that are directly responsible for protecting the inauguration - Capital Police, the FBI and Secret Service.