It's because the quality of footballers has vastly increased. Somebody as technically gifted as Arnoutovic or Dimitri Payet wouldn't be playing for mid-table teams a decade ago. Players in the prem are also 30% fitter since Wenger. I just think that there are a lot of top players out there.
Imagine my surprise when I saw Steven Defour in the Burnley line-up. Yes Steven Defour. Its amazing how even the smaller clubs can snap up such good players due to EPL riches. Payet at West Ham. Cabaye at Crystal Palace. Shaqiri at Stoke. None of them would look out of place in the top EPL sides.