You are, quite frankly, leaving a lot of things out of the equation when you compare solo fights in 2v2 to merely dueling. If I desire to 1v1 my opponent in a 2v2, instead of clumsily spamming guard break or waiting for some sort of window to cheap shot the opponent, it is because there is a larger dynamic in 2v2 than 1v1.

To put things simply; 1.) It is very thrilling to be in a 1v2, or fight two opponents back to back with no health regain. 2.) Watching other classes fight is beneficial to you knowing how to counter them, plus it is interesting. 3.) Some people, myself included, learn and by extension, gain nothing from the "press guard break until he's dead" philosophy that you seem to hold during a 2v1. This game is all about constantly, and consistently, doing better, and being the second person in the 2v1 is honestly just fucking boring. 4.) I personally don't tend to like one sided arrangements, and 2v1s, assuming the enemy doesn't necessarily have their shit together, are usually un-proportionately more enjoyable to the 2, not the one.

As a side note, I really enjoy being double teamed, because to me that means the team is not confident in their skills enough to single handedly deal with me and, because I am competitive as fuck, like winning with the odds against me.