Web apps could, potentially, de-monopolize mobile devices. But what's the point? These devices are generally considered disposable. Most consumers (approximately all of them, in fact, aside from a few hard-core OSS and hardware hacker types) don't see any negative impact from these "monopolies".

Aside from that web app technology is of poor quality in almost every important domain: architecture, efficiency, stability and security. "Native" mobile apps have overlapping problems in these domains, too, but web apps are generally going to be strictly worse. No thanks.