Why is the back so rarely involved in scabies?

Why is the back so rarely involved in scabies?
G Ital Dermatol Venereol. 2018 May 16;:
Authors: Veraldi S, Schianchi R, Esposito L, Pontini P, Nazzaro G
PMID: 29781261 [PubMed - as supplied by publisher]

Source: Giornale Italiano di Dermatologia e Venereologia - May 23, 2018 Category: Dermatology Tags: G Ital Dermatol Venereol Source Type: research