5 card draw for high--too easy to milk the fish?

[WordWhiz]

Someone asked recently on RGP why regular 5 card draw isn't played much anymore. One person responded that it was too easy for the pros to win. That is, there wasn't enough luck! An inferior player would walk away a winner only in only about 10% of his sessions, and would soon realize his inferiority and stop playing. Whereas in Texas Hold Em, a fish can play for quite some time before realizing he's getting the worst of it, due to the tremendous amount of luck involved and the huge swings. If true, this makes sense.

What I'm wondering is why it's true? What is it about draw poker, a game of virtually no information other than number of cards drawn, that makes it so easy for the pros to clobber the fish? I've skimmed through Caro's section on 5 card draw in SS1, but nothing makes it really clear why the game is more beatable than Hold Em or Stud or Omaha. Thoughts?