The biggest gaming store is almost certainly the Android Google Play Store's gaming section. It also wouldn't surprise me if the nintendo eShop is larger than the steam store, but at the very least I'm very confident in Google Play and iOS app stores being larger than steam for games.
I think the majority of gamers have never played a PC game or watched esports. The parent post only said "I even played games", and you jumped to "watching esports" and "twitch". Watching esports is a tiny niche of gamers. Watching twitch also is.