Web browsers have more or less become mini operating systems, running elaborate virtual machines. There's way too much complexity for everyone involved — from web devs and browser devs to the users and the people who maintain the standards, then there's the devs who have to make native clients for the web apps — just to deliver products that don't have half the power of OS-native software. Everyone has to keep reinventing the wheel, like with WebAssembly, to fix problems that don't have to be there in the first place, not anymore:
Thanks to smartphones, people are already familiar with the modern concept of the standalone app; why not just make downloading an OS-native binary as easy as typing in a web address, on every OS?
Say if I press Cmd+Space on a Mac and type "Facebook" in Spotlight, it immediately begins downloading the native OS X Facebook app. The UI would be described in a format that can be incrementally downloaded, so the experience remains identical to browsing the web, except with full access to the OS's features, like an icon in the Dock and notifications and everything.
TL;DR: Instead of investing resources in browser development, Android/iOS/OSX/Windows should just work on a better standard mechanism to deliver native apps instead.