The hosts struggled to tackle the awkward pitch in Cardiff, eventually getting thumped in an eight-wicket loss.
England hit 211 runs, which Pakistan chased down with 77 balls to spare, and Morgan believes that his team were at fault.
"One thing we didn't do was adapt to conditions; coming from Edgbaston to a used wicket, Pakistan did that well and played better," Morgan said during the post-match presentations.
"We did prepare, Pakistan bowled well but we didn't adjust and 200 isn't competitive, 250-270 would be a good score. We bowled okay but 200 was well under par. We continue to learn, everything we did was calculated, but Pakistan had played on the wicket previously and that helped. You have to adapt in knockout cricket, so it's an important lesson."
Pakistan will face either India or Bangladesh in Sunday's final at The Oval.