Every food commercial, advertisement, and packaging in the US is currently protein obsessed. I just bought 3 burritos, and the most noticeable thing on the entire package is its protein content. TV commercials about waffles are advertising that they have X amount of protein per serving. The products in my jobsite's vending machine have protein all over every package.
So while it sounds insane for detergent to label itself gluten-free, for people with severe gluten sensitivity toiletries, cosmetics, and other non-consumable items can still cause them symptoms with exposure, or so I've been told by someone I know with gluten intolerance. Whether this is an exaggerated concern or not, there is demand (albeit small) for such products.