Could you please expand more on this?
As far as I know, modern browsers support notifications, so in this regard there is nothing that such apps offer that browsers don't. Further, I'm not sure if in-app advertisements are somehow different from same advertisements presented on a web page (if what I think is what you mean, of course).
I think "the devil is in the detail."
While browsers also support notification, it is a relatively new technology. It also needs consent before it can be used. I haven't for once click "yes" for that matter. While in apps, push notif is on by default (opt-in by default) << CMIIW; this was when I worked as a mobile apps tester years ago so that it might be outdated.
For ads, google has AdMob for mobile apps and AdSense for web content. Of course, it has different pay rates, size, video capability, etc. In freemium games, users can be "forced" to consume ads to get more playtime or power-ups. Also, It's more difficult to block ads on apps.
However, in the future, maybe casino operators would create such a business model so they will be benefited from mobile apps.