For many crimes, especially violent ones (which, considering 5 deaths and over a hundred injured, I’d say this qualifies)

Yes, and the people directly responsible for that violence were arrested as quickly as they could be identified and located. It's like you simply refuse to accept that assigning culpability is not so straightforward when it's several degrees removed. Mens rea in a criminal conspiracy requires an overt act to commit a crime, and the overt act must be verified, else a charge wouldn't be provable in court. And no DA in the country would arrest someone that high profile in such a complicated case without gathering evidence, interviewing witnesses, crossing t's, and dotting i's:

Whether a decision about Trump’s culpability for Jan. 6 could have come any earlier is unclear. The delays in examining that question began before Garland was even confirmed. Sherwin, senior Justice Department officials and Paul Abbate, the top deputy to FBI Director Christopher A. Wray, quashed a plan by prosecutors in the U.S. attorney’s office to directly investigate Trump associates for any links to the riot, deeming it premature, according to five individuals familiar with the decision. Instead, they insisted on a methodical approach — focusing first on rioters and going up the ladder.

I don't know what world you live in where the DOJ can simply act like John Fucking Wayne whenever it wants, but these are career prosecutors, and thankfully they're not dumb enough to try to lock up the kingpin before closing the net around the underlings and making sure the case is ironclad.