They do it because they can. There's not a lot of people creating high-quality fonts. If you've ever tried looking for free fonts, it quickly becomes clear that

They do it because they can. There's not a lot of people creating high-quality fonts. If you've ever tried looking for free fonts, it quickly becomes clear that the quality is often lacking (inconsistency, missing glyphs, poor spacing/kerning). And then you find that it's not even free anyway, just 'free for non-commercial use'. We'd see similar restrictions on licensing for other 'tools' (compilers, maybe?!), if there wasn't so much competition including open-source options.