The actual salt (sodium chloride) content of w-u-l is small, but many will steer away from it. SLS - Sodium Lauryl Sulphate - (or other foaming compounds) are used in many car shampoos, but can be a skin irritant.
Like shampoos and soaps for human use, they remove oil and leave the skin dry and itchy.
Further, there are environmental concerns over the production of SLS, so some manufacturers are moving away from it and swapping to more eco- and human-friendly options, both for car care products and soaps and shampoos for us.