I can only assume this is related to the fact that Max Knuckle and Max Ooze increase your Attack and SpAttack (respectively) each time you use them. Not just for the Pokemon using them, either -- it boosts all 4 Pokemon, if they have hitpoints. Further, it's not restricted to just that move, either. Any other moves you use will benefit from that stat boost, as well, including other Max moves.
Compare that to Max Geyser, Max Flare, Max Hailstorm, and Max Rockfall. They start the corresponding weather condition. Rain and Sun will alter the output of Fire and Water moves, sure, but it doesn't keep stacking. And it affects all Pokemon equally -- both your allied team, AND the Raid Pokemon.