Most horses would be trying this week. It is the weaker meetings that you spot 4 dodgers a race.
I think you will find that English racecourses are the same.
I think there are two possible explanations of the ride:
1. Carberry didn't want to give Muirhead a hard time too early, especially for the reason Sheikh outlines above. He felt he had a good horse under him, and that he would be able to catch the tiring leaders, who weren't that good (as you outlined when tipping him at 6/1). He misjudged things slightly, and the horse stayed on by a diminishing two lengths, looking as if he might have gotten up if he had taken closer order (he was last 3f out I think).
2. Carberry was told by Meade that today was not the day, to give the horse a nice ride and get him enjoying himself. He ambled the horse out the back for 2m3f, and then realised that things were starting to look bad. So he started to get serious on his mount and (being clever) rode hard all the way to the line, thus ensuring that he couldn't be accused of not trying.
I weigh the above probabilities as 70% to 30%, especially given Meade is far from the worst at this sort of thing, and given Muirhead's unusual CV.