They’re getting smarter about this. Instead of charging Trump immediately they’re saving him for after all his conspirators are convicted. They know that Trump will leave his people out to dry if he thinks it won’t impact him, and by leaving Trump out of it the guilty verdicts become significantly easier to achieve. Once they’ve got a whole slew of air tight convictions to point to their case against Trump becomes really simple because they just need to show be was working with all these people which is practically a matter of public record at this point.