It's an odd one. I don't think you can point to just mental weakness if they came back from getting thrashed in the first test to win by 400 runs then we came back from that to win by 8 wickets in under 3 days. I really do think at the moment both sides are over reliant on brilliance from a couple of players. Both bowling lineups look strong but both batting lineups have too many players either badly out of form or just not up to test level.
It's a common theme though. Both teams have kept thrashing each other over the last few series, going back to 2006/7 really. There have been few really close matches since the 2005 series. Even in 2009 although it was 2-1, we beat them by 100 and 200 runs, they beat us by an innings. 2010/11 we won 3 tests by an innings and they won 1 in the middle by 250 odd. 2013 the first test got a lot closer than it should have done when they had a big 10th wicket partnership then we won the Lord's test by a similar margin to what they won by this time. Just seem to keep thrashing each other.