Based on their Play/App Store screenshots, I suspect they're looking for games to put in their app, and being able to embed HTML is simply easier for that. But I could be wrong - I have no association with this.
While we do have the native app in the stores, WAM is a PWA ( Progressive Web App ) and is built using web tech with the purpose of publishing HTML5 games. We believe HTML5 games have a lot more punch than they're given credit for and just want to see amazing things being created on the biggest platform in the world: the browser ^^