Because he hasn't been found out at first-class level, he's too good. He's not be the first player to have flaws revealed only at the very top level. Test cricket is not the ideal place to work on weaknesses, and I'd have Marsh in the side instead, but that's not the way they've gone. I would like to have seen him given the chance to work out his game at the lower level but now that they've picked him again doing that would be deemed dropping him for a second time. Between now and August he needs to work on that back foot and those outside-off jabs. I think the selectors have wasted the chance to blood a talented bloke like Marsh, while giving Hughes the time to work on his game at Shield level.
... against Pakistan in England in July.
Many more than that I'm tipping.