Why does nobody understand that Amon wasn't severing people's bending abilities? Only blocking them.

Seriously, how has this gone over so many people's heads?

To permanently remove bending, you have to be able to energy bend. The only person who can do that is the Avatar. Amon was just using psychic bloodbending to do an enhanced chi-block, and copying the energy bending stance to enhance the illusion.

Aang showd that the Avatar state makes you immune to bloodbending, so it makes sense that once Korra was tapped into her spirituality, she was able to easily undo the effects of Amon's bloodbending.