Why EU nations more fit than the SA teams?

It was clear for so many games, especially those that went to ET, the EU teams actually were far more fit and looked to be able to keep the same level until the very end, whereas the SA teams, African teams that were supposed to be more familiar with the climate looked exhausted in some cases. I found it strange to see Netherlands players running non stop while opposition could barely walk.

It was supposed to hinder the EU team's chance at this WC.

So why do u think that is, the players just being more fit through harder training? More determination and mental strength to push the body? Its not like the SA and African teams are not players from the top leagues and clubs and dont train hard....

Maybe some of the European teams were so afraid of the Brazilian climate that they put double and triple work into fitness to be able to overcome it?