It appears that when we're looking to go our for Mexican food here in the United States, we prefer Taco Bell over ANY other "Mexican Restaurant". Of course this is according to a recent poll that has come out.
Taco Bell beat out Moe's and Chipotle or any other Mexican food chains. Keep in mind this poll takes familiarity of the restaurant, quality of the food, and future consideration for coming back and eating there again into consideration. So you may know of a bunch of places with better Mexican food but they're not all over the country. So I guess this all makes sense now.
Don't get me wrong, I love me some tacos from Taco Bell but as a country I'd say we look a little silly voting them the "Best Mexican Restaurant".