Theres numerous reasons why these players didnt perform to the standards the fans/press expect, several have been mentioned above.Others are:
Messi was excellent in the games bar
germany, goals arent the only measure of a good performance. He made numerous assists for Higuain in the group games and with a bit more luck would have had several goals himself.
Ronaldo is the only outstanding talent in the attacking half of the
portugal team, this was shown up against Spain where they neutralised him and thereby the team. Portugal set up very defensively with the hope a bit of Ronaldo magic would win them games, it didnt happen bar the N.Korea game.
Rooney was still carrying the injury Utd had rushed him back from to try and save their season, plus for England the formation doesnt suit either him or Gerrard but seems to be set up to play all the big name players, rather than focusing on the 'team'.
Kaka hasnt had a good season for 3 years which is probably why Milan were delighted Madrid stumped up 60m for him. He also missed large chunks of the season with an injury which doesnt help you build form.
brazil's problem came when Elano got injured as he was pivotal to that Brazil sides attacking contingent.
At the end of the day the World cup is only 7 games which is nothing in a season for footballers, theres no time to really find form if you aren't coming into the tourney with any. Also a good world cup not a great player makes, look at the likes of El Hadj Diouf, Roger Milla. Hell Podolski and Klose have had great tournaments yet havent been able to get much of a game for Bayern for the last couple of years.