As a collegiate soccer official, I can almost tell you what is going through the officials' minds.
1) They don't want to involve themselves in the game too much at the start, so they are not going to call much in the name of "letting the game flow".
2) The teams then proceed to beat the crap out of each other, and the game starts to careen out of control.
3) The officials then recognize it, so then they start calling every touch making an attempt to bring the game back under control.
Whether officiating assignors want to admit it or not, they don't want fouls called early. They want to see officials "manage" the game instead of calling the fouls that need to be called. I am the opposite of above in that I'll call games tight early and then adjust if the players adjust. That's not what assignors want, because that's not what coaches want and ultimately assignors work for the coaches.
It's not right, but it's reality. I wish assignors would be backed to support officials calling more fouls before games get too physical, but that's not what's wanted at the collegiate level.