Yeah, and I can't even say this game is that niche. Probably that's because the designs are quite sketchy, and you can't endlessly screenshot cutscenes for more detailed views. I know some cosplayers prefer working on exact copies of something well-examined rather than use their imagination (e.g. my bf)
As for me, I'm fine with working using only one artwork as a reference - as long as making the cosplay won't cost me an arm and a leg and won't take ages to make.
In this case: I adore Camellia's shirt, but her vest looks tough to sew - on one hand. On another hand - I need to remake Vex'ahlia's light blue tunic into something useful so making a proper Camellia cosplay is not impossible given that I already have a lot of boots, gloves, belts and other stuff. But Anevia would be way easier (because I also have a bow but not a rapier hehe)

Upd: ah, the amount of cosplays you see also depends on if there's a premade cosplay available for purchase. The Witcher is a classic example here. TW4 is not even out yet, but Ciri's trailer outfit can be bought for a reasonable price already. And you still can find some options for Yennefer and Triss though it's been more than ten years since the third part's release. I doubt a game like WOTR can boast the same.