I disagree and in my opinion you are looking at it the wrong way by just assuming big group = slow pace. Often it is, but you can see when the speed gets turned up wheter it's been a hard effort or not. When it's been hard it blows up directly when someone put the hammer down, when it's not been hard a lot of them can keep up for a while after the speed goes to the next level and the splits are coming later and they are smaller.
If it had been one of those pretty standard "a bit cozy" masstarts, that we often saw back in the Northug days, those guys being in 10th to 25th would've likely been fresh enough to maintain the increased pace and kept in contact until the stadium hill at 17 km.
The fact it blew up in the easy part on the last loop shows in my opinion that it was a hard race from the start and that maybe more than 20 of those 31 guys in contact (within 13 seconds) after 3 laps were already at the limit or very close, meaning they had no chance to increase the speed when Krueger put the hammer down. Strong guys like Musgrave, Lapalus, Nyenget, Klee etc were in great position when Krueger went to the front, but they had no chance to step it up, because the total load of the race already had been high.