If the investigation was serious he would have already been charged with more serious crimes involving alot more countries. It's a shot over the bow to make sure he exits quietly. If they want him to step down and let Harris be President it will get louder.
President Biden is still angry with top Democrats who forced him out of the presidential race, even just days away from the Democratic National Convention.
A plethora of investigations could have been conducted in the time they have spent stonewalling this one. They are using it to Control Joe Biden. They being Garland's people because they want Harris and Walz in charge so they get to run completely wild.