Because newspapers are not forced to give out their news for free. But they have to give you an alternative to selling your data; taking money from you in this case.
Valve being a cool company might be true and all but I think there’s also the real reason that steam makes money by selling games, and making it easy for users to stick to gaming (with steam) ensures ongoing income. Imagine someone who now loves gaming on TV but being annoyed by their broken steam link - what are they going to buy next? A PlayStation and years without a game sold to them.
Average website visit in 2024 (i.imgur.com)
8 Years later my Steam Link is still getting regular updates (slrpnk.net)