I'm not really sure how that logic follows, as games are also just applications, and although the web was not designed as an application platform, but rather as a hypertext document browsing / delivery platform, yet people managed to wrangle it into performing fairly decently as an application platform, so why not game engines for application development? (I've actually seen more than a few really interesting and useful applications built in Godot and other game engines already, and I'm quite sure more are coming.)