Its grandstanding and posturing.

But there is actually a good argument. Someone who the DOJ have decided wasn't worth the hassle to properly investigate might still be identified and reported by a co-worker or neighbor. Which then begins to force the DOJ's hand (they are still cops so they might ignore it but...). I personally think everyone who crowded outside the building deserves to be locked up, but I can see an argument that only people who entered the building or who actively caused damage should be charged.

Because yes, facial recognition and DMV databases are already a thing. But, much like with a red light ticket, a decent lawyer can work wonders to argue out "a robot claims that I commit a crime". Whereas having a human in the loop removes that gotcha. Hell, if my cousin is any indication, you don't even need a lawyer to argue against a red light camera or an automated speed trap and just need to care enough to show up to the courthouse for a few hours.

Also, regardless, this is indeed (attempted) obstruction of justice to protect insurrectionists.