Universal design means building a space that works well for everyone, regardless of age or ability - curbless showers, comfort-height toilets, lever-style faucet handles, and good lighting are common elements that benefit any homeowner, not just those with mobility needs, which is why the category has broader appeal than "accessible bathroom" framing alone.
Marketing this as a design philosophy rather than a medical necessity broadens who it appeals to - many homeowners want these features simply because they're more comfortable and more resale-friendly, not because they currently need them.