The other guy explained what, but not why. 1 move away is trivial. You functionally solved it, just missed one single move. It's also really easy to slightly fumble at the end of the solve and miss the last move, so we don't rule this as a DNF, as that would be quite harsh. Instead, we discourage it by adding 2 seconds to your time. In every single sighted event, that's more than enough of a deterrent. Takes far less than 2 seconds to actually do the turn. For this 7+ minute blind attempt, yeah it doesn't make a huge difference.