Why can't Nicky Henderson win the Grand National and Willie Mullins a handicap chase at Cheltenham? I may have the answers

Every year two facts never cease to amaze. First, why can't Nicky Henderson get a horse to run well in a National of any description. Second, why can't Willie Mullins win a handicap chase at the Cheltenham Festival?

Henderson has won two Gold Cups and three King Georges over staying trips. Last month at the Cheltenham Festival he saddled a 1-2 in the Pertemps Final over  3m, so it's absurd to think he can't win a National of some description, particularly when trainers who aren't fit to lace his boots have enjoyed success in such races.

The obvious explanation is that he doesn't acquire the right type of horses, but I'm far from convinced that is the case as he trains loads of horses with stamina- laden pedigrees. A more valid reason is that Henderson's training methods don't suit marathon chasers and he only runs horses in these races as an afterthought, when they have proven they aren't good enough at shorter trips. Perhaps they run in Nationals when they are past their best.