You might similarly ask why app stores on iOS and Android are such a big deal, and why Steam is even a thing. It's because deployment is a harder problem than

You might similarly ask why app stores on iOS and Android are such a big deal, and why Steam is even a thing. It's because deployment is a harder problem than development (at least, it's harder for developers, because deployment is a social problem). The web is a pretty poor development target (though it keeps getting better), but it's a damn terrific deployment medium, and that's a winning tradeoff.