Have you ever noticed that most of the specific grooming/dress rules are defined and enforced by local elder bodies? The WTS leaves it to the elders in each congregation to make most of the "rules." For example, in one circuit, if you attended one congregation, sisters could have 2 piercings in the lower earlobe, in another the elder body would make the sister stop using one piercing. In one congregation, no brothers with privileges could have a mustache, if they switched to a congregation 8 miles away, they could have a mustache.
I think it is no accident that the WTS does this.