I absolutely agree that this is 100% possible with HTML5, and the only we’re not seeing it happening on a massive scale is a because of a cultural blind spot - as evidence, most of the comments in this thread. The technologies we have now, like Phaser, are vastly superior for building games for the web than Flash ever was (I was a full time game developer for 10 years, and a full time HTML5 game developer now.) And I believe it’s actually easier to monetize these using Stripe than through an App Store. Your game lives on a URL, which is just click away, and paying for it is just one more click - this is about 10 seconds of work for a user. And, you control 100% of your business from production to distribution. There’s a huge pile of money lying on the table here for anyone who can see this.
2. The reason we don't see them anymore is because it's far easier to monetize them on mobile.