If you operate a punitive regulatory regime with respect to cross-contamination, you can't expect manufacturers to say "OK, we'll take the occasional fine and public-relations hit just to address this tiny part of the market" if that's not good business.
If you buy cotton cleaning patches for cleaning rifles, they come with Prop 65 warnings these days. Not because cotton causes cancer, but because cleaning your rifle can expose you to lead, and because plaintiff's attorneys can sue in private enforcement actions. So does the rifle, the solvent and the brass cleaning rod.