First of all, because of course he is...
Secondly, how was throwing the book at Derek Chauvin going to ensure that the Floyd family was better off?
Obviously, the difference between these two cases is that Chauvin was clearly innocent and yet remains a political prisoner receiving a far harsher sentence then Anthony, who should be sizzling in Hell by now.
Punishment is not simply about providing the victim's family with closure and comfort, it's about mitigating the likelihood of such acts of barbarism going forward; the more severe the punitive consequences for X action, the less inclined people are to take X action. Societal instability is directly proportional to the leniency granted to those who break the rules. This subversive fuck is literally challenging on of the fundamental pillars of a function civilization.