Why do so many want the new Chaos Space Marine Raiders to be Primaris scale?

First let me say I am not trying to start an argument and I'm not a Space Marine fanboy or a Chaos hater. I have a Red Corsairs Chaos Space Marine army and I'm not too fond of Space Marines. I'm just curious about this.

I see many posts and comments on various Warhammer related subreddits about wanting new Chaos Space Marine Raiders to be Primaris Scale. But shouldn't they be smaller since the models are all Firstborn and Primaris are canonically larger than Firstborn? And while I could understand some other Chaos Space Marines models being Primaris scale due to being juiced up on Chaos magic the new Raiders are specifically said to not be fully corrupted by Chaos yet so shouldn't they be smaller than Primaris from both being Firstborn and lacking Chaos enhancement?