There are many reasons frequently cited by safety directors as to why they answer the fabric question first.
1 Protection
Protective performance ratings (ATPV, or Arc Rating; NFPA 2112, or flash fire rating; etc) are based entirely on the FR fabric. We don’t get a rating on a blue shirt or a red coverall; the protective designations are fabric brand and weight specific. All single-layer garments made of that particular brand and weight of fabric will then carry that rating, regardless of garment type, manufacturer, color and so on.