Ask HN: Why PGP isn't built into all modern browsers?

Web browsers are used for communication by billions of people. One would think that with all the privacy and security issues facing individuals and companies on the web today, client-side encryption and signature verification would be the topmost priority for all browser vendors. Yet it's not the case.

Browser developers are in a unique position to solve the chicken-and-egg problem with client-side cryptography. Namely, it is only useful if a large portion of people you communicate with has it too. (This is not something that a standalone app or a plug-in can solve.)

I'm not aware of any attempts to tackle this problem by any of the major vendors. Are there any well-known reasons why? Are there any publicly accessible discussion about this among browser developers?