Libertarians only care about 2 things: lowest taxes possible and legal weed, and they would gladly sacrifice the latter in favor of the former. Anything else is nothing more than lip service.
Universal healthcare means taxes, and that is the one thing Libertarians hate above all. Never mind that it would be cheaper than private insurance. They relish in the fact they can skip buying insurance, and if they get hurt, ERs are required to treat them anyway.