Because he's still in office and Muller has made it clear; no indictments of sitting presidents (such a thing could be used as a political weapon). He's clearly listed as an unindicted but criminal person, there are sealed indictments that likely include Trump (to be unsealed once he's no longer protected by his office) and the CA AG and NY AG both have cases against him, CA for election shenanigans in '16 and NY for money laundering and mob connections. The Senate (under solid Repub control) has also made it clear that they'd vote to convict in the event of impeachment in the House so long as it was a secret ballot, meaning they believe their own president is guilty of felonies and misdemeanors.
Trump is fucked once he's out.