While it is free to download it, the license still costs. Though they seem to let you use it unlicensed for an unlimited amount of time with some restrictions (like not being able to change the background image and an ever present watermark). At least this was true for windows 10. No telling if/when they will drop that feature though, especially if loads of people start using it unlicensed like that (though I doubt that has any effect on people using it that way or not).