Probably when you make real art you love you want as many people as possible to see it.
Also if it was paywalled, I'd totally scrolled by, because the front page didn't sell it to me. But it's free, so I didn't, so I played and returned to buy it, and so did many others.
It seems to work like the marketing strategy in the music. And the Devs come from the music, they're on Spotify.