Because if the team plays more poorly than it would otherwise on the road because of it, then it's hardly an advantage in its entirety. It's an advantage at home, and a disadvantage on the road.
No, that's not what I'm saying...look at it this way. Say you have a team that is usually 5-3 at home and 4-4 on the road...then because of a crazy good homefield advantage, that team goes 7-1 at home and 4-4 on the road...how is that a bad thing?
You haven't proven that a team with a strong home field advantage plays worse on the road if they are talented. You showed Seattle who had the definition of a mediocre team with great home field advantage until recently. You may or may not be right. However you would need a greater sample size which takes into account QB play and team talent.
