Simply put -- consumers can't be trusted to be able to deal with complex secure authentication schemes. That's why there's so many easy-to-guess "What city did you grow up in?" password-reset functions. There are so many weak links in the chain of trust, it takes a concerted effort on the individual's part to secure it.
The CEO of Cloudflare fell victim to this when someone CONVINCED AT&T TO REROUTE HIS VOICEMAIL, starting a chain of events that wound up with the interloper having complete control over Cloudflare and the myriad of sites that use CF (and therefore trust it to send legitimate data).
It's a bit exciting/fascinating to read about the chain of events, (particularly the timeline):