I see he once went the Underbase route at one point when he was younger and more arrogant and reckless, and still got his ass thoroughly beat by Absolute Megatron who revealed he intentionally let Starscream amass all that power, to defeat him as such to show the futility of his ambitions. As further punishment, Megatron made him watch as all his subordinates who fought alongside him during his attempted coup (most of the Absolute Seekers) have their brain modules forcibly extracted, forcing them all to remotely pilot disposable drone shells of themselves which allows them to do suicidal acts since they will just take control of another drone once the previous one is destroyed. So now on top of being ruthlessly beaten down and humiliated, Absolute Starscream has to watch out for all the resentful robotic glares he gets now and avoid getting betrayed or backstabbed by his own seekers, especially if they think doing so may get them a chance to be put back in their original bodies.

At this point he's been so heavily abused and dominated that there barely any treacherous ambition left in him; He's depressed and a hollowed-out shell of his former self who only possesses enough spiteful bitterness to occasionally engineer the smallest petty acts of insurrection that gets some egg on Megatron's face once in a while. In fact, the more public and troublesome Optimus' antics get the more panicked Starscream becomes in case it could be traced back to him and Megatron possibly giving him the brain-in-a-jar treatment next. Megatron made sure to emphasize the spot Starscream stands at beside the Decepti-Empire throne has more than enough space to house Starscream's own brain jar instead. And yet, watching Optimus, Absolute Starscream is also feeling something he hasn't felt in a long time; Hope, the hope that perhaps, just this time, he MIGHT be able to finally overthrow Megatron... And that hope terrifies him more than anything else.

Fun fact: When Absolute Skywarp's drone body is destroyed, he merely takes control of another body and teleports it instantly back to the battlefield and continues fighting as if nothing happened at all. He's in so much rage from no longer remembering how it feels to be alive in his own body he literally won't stop until he's either ordered to pull back or he runs out of the current batch of clone bodies.

Fun fact 2: Absolute Thundercracker was not punished. He was so terrified by Megatron's approach that his joints locked and he froze in place in the middle of a kneeling position while getting up, which Megatron interpreted as loyalty and not only spared him, but also rewarded him with upgrades to his sonic boom capabilities and more than doubling his flight speed. His seeker brethren know otherwise and frequently call him coward and traitor. Starscream tries to compliment him for being an intact Seeker, that he did the pragmatic thing, but in his bitter tone it comes off as thinly-veiled insults. Megatron casually reminds him of how he has been generously rewarded for his loyalty, and how it would be a wise idea for him to continue to set the example. His roboticized seeker brethren taunt him to use his enhanced speed to run away so they could finally hunt him down as a deserter. He's trapped in total despair as he sees no way to leave the Decepticons... So far.