This argument really annoys me.
Wigan are kinda like Walsall, only instead of being sandwiched between Birmingham and Wolverhampton they are sandwiched between Liverpool and Manchester.
They were non league until about the time we last won the title, and then they spent 20 years hanging around in the lower divisions. If you happened to be from Wigan and over the age of lets say, 25, and your house is barely 15 miles from Anfield, or Goodison, or Old Trafford or Maine Road then can you really be blamed for supporting one of those clubs? Ditto if you are from the areas immediately surrounding Wigan then your local team is probably going to Manchester United or Liverpool or Everton or City or Bolton. You aren't going to support Wigan. They are utterly **** by geography. They probably have the smallest catchment area in the English game.
Compare that to Sunderland (who you used as an example) who really only have one local rival then it's pretty obvious why the gates are so different in size. If you live in Sunderland then you are closer to Edinburgh and Glasgow than you are to Manchester and Liverpool so if you want to go to a game then you support one of two teams or you have a six hour round trip for every home game. I'm not sure why a club is more deserving of Premier League football because it has fewer local rivals or a bigger catchment area.
Yes and Wigan is more famous for Rugby and George Orwell really. They were a non league club until 1978 and it wasn't until Dave Whelan took over they made progress through the leagues. Many people may dislike him because he's outspoken but what he has done for that football club is fantastic. The population of Wigan is only 81000 and they took nearly half that to Wembley. So its very unfair to knock them just because they are small.