That was exactly what got explained to me by MPP, UP, the folks that did my suspension, and my back of napkin geometry sketches.
as a neophyte to suspension but an engineer, I wouldn’t describe it, as “better handling”: a negative camber (wheels angled outwards as you get closer to the ground) makes it such that, under higher lateral centrifugal force of a turn, the outer wheel is forced to create more contact. This is compared to what would happen if it was straight down where contact would get less the more lateral gs you are pulling, which would make it loose grip and skid or something bad especially in quick turns eg moose test.
Maybe mpp can explain better the side effects of not doing it. I also appreciate that as a vendor they have to be cautious in their language about what is recommended, required, etc.