Unless as has been said, the refs were under instruction to go easy on the yellow cards so none of the stars would be out of the final rounds except here it backfired with Neymar’s somewhat freak injury. They had to give the one yellow card to Silva.
Refs that call fouls early on for pushing, grabbing and shoving usually don’t have to deal with the kind of actions that result in many cards later on.
Geiger has called fouls early on in matches and the players responded by not engaging in rough play. I think the players actually like it when rough play is not tolerated; especially the more talented ones. Geiger has gotten great reviews for his management of the matches to which he has been assigned.