Mueller is just doing this to give the media some legitimacy to use the words “Russian” and “election” in one convenient news story...
Naw. He knows he has to find something, and wrap this up cleanly. The “Russian conspiracy to interfere in US elections” has been found, participants indicted, and Trump exonerated. That narrative is over; like a decapitated chicken, it may keep moving, but it’s dead.
To go after the big fish, you first have to catch small fish to act as tasty bait for ever larger fish. This indictment explicitly released the minnows, while keeping the eels which are neither good bait nor good eating.