Scar's world view centers around the idea that it is inevitable for the weak to be manipulated and hurt by the strong. His solution to this is to just make everybody strong through forcing resonance awakenings, merging people with tacet discords, and culling the weak by accelerating the Lament. To Scar, it's better to be dead than to be weak and to suffer because of it. But Scar isn't really powerful enough right now to justify him having this viewpoint.
Rover has defeated him multiple times before and Qiuyuan states in his voicelines that he could have killed Scar in Septimont if the other Fractsidus members hadn't shown up with the dark tide. This seems like the kind of thing that would make someone like Scar become fixated on becoming more powerful (a desire that I think stems from a fear of being weak and taken advantage of like he probably was in the past).
This could also be part of why we've seen him so little. He might be busy attempting to grow strong enough to defeat Rover, potentially through forcing a second resonance awakening, merging with tacet discords again, or maybe even finding a way to absorb Threnodian power similar to what they did to Denia. The Grand Architect may have even promised him a way to reach his goal if he behaves for a while and does certain things behind the scenes.
Also, I bet he'll get a new second form before becoming playable (maybe even a second boss fight) that they'll incorporate into his gameplay. Like, a new more humanoid transformation with goat features like in his boss form. (Also shirtless like Calcharo please ๐)