The people who want it most (will pay the most and will pay immediately) are advertisers. Which means the apps that want it most are those that have loyal users, but have been unable to effectively monetize them to advertisers. There are plenty of applications for it outside of ads. To extend your question - why would you truly want to link out to another webpage in someone's browser? That's what AppLinks/OmniLinks/DeepLinks are designed to do - to make the relationship between app use resemble the relationship between web pages.