I think it's both Jules.
Re the latter; it's safe to say from what I've watched that the real hunger that got this England side to the top over the last 3 or 4 years has subsided, which is only natural. Certainly, the edge that guys like Swann, Anderson, Trott, Prior, etc had3 years ago is gone. I'd say backing up in Australia 6 months after the last gruelling series with relatively little to still 'prove' is a major factor too.
And for the latter; tactics and decision-making yes. Guys like Cook, KP, Bell, Prior who can quite clearly bat with anyone in the world have just thrown their wickets away. I've gone on record in earlier pages about Cook's in game captaincy and field positions at times in the first 2 tests which have been diabolical, and then a succession of little things which all add up; dropped catches, being on the brunt of sledging, Trott, etc. Everything is in Australia's favour right now, but they've made their own luck too.