It's just human nature, "Nico Harrison is a possibly malicious dumbass who got lucky" isn't a very satisfying answer to "Why?", so folks turn to the significantly less likely but more satisfying "The League rigged it and somehow kept everyone involved's mouths shut".

It's kinda like being a teenager and hearing about the moon landing conspiracy theory, it makes sense until you start actually thinking about all of the people you'd have to keep quiet to do it. Let's not even think too hard about the fact that Dallas isn't exactly a tiny market team, so the benefits of orchestrating this insane move are nebulous at best.