> Why should they optimize for the <0.1% of people who don't have JS enabled?

Because their competitors do that.

Most counts place non-js users (which is not always their choice) between 1% and 4%.

That means that for every 10,000 users, there will be between 100 and 400 that don't have js enabled. It's been estimated that buzzfeed, which we use as a traffic example, gets over 10 million requests that don't support js per month.