There are a ton of terrible things that are popular. KC Masterpiece sauce is the most nationally popular "Kansas City" BBQ sauce even though it is hot garbage.. Bud Light = most popular beer in the world. Pizza Hut=most popular pizza place in the world. If OK Joes had better than B+ barbecue they wouldn't be slathering it with cheese and deep fried crap.
Also, lol at OK Joe's being the #1 bbq place in the world. Aaron Franklin would like a word.