7.1 is the standard theater/home theater speaker setup because those speakers need to play across a crowd of people. By necessity, you cannot use only two speakers because of how everyone is positioned differently. 7.1 delivers a "good enough" product across a wide space.
However, headphones are different because they address only one set of ears. Therefore there is no need for many speakers. Modern day virtual is superior because audio engineers have access to extremely precise models of how human hearing works. For example, there are audio tracks like
this which use only 2 microphones positioned where a human's ears would be to capture the sound. When this is played back from headphones, there is no need for more than 2 speakers because it is playing it back exactly as the ears would have heard it normally.
Another way to put it: if 7.1 headphones were superior, then why do top-of-the-line headphones like the Sennheiser 800, Stax SR-07, Audeze LCD-3, etc only use 1 per ear?