I'll add that Krop didn't intentionally cut off Fisher. No one uses their legs on the back part of their stride to cut into someone. That would be asking to trip yourself. He clearly didn't see Fisher. Fisher could/should have anticipated that, being in Krop's blind spot and it being on a curve with Ingebrigtsen leaving the curb open by pulling away. Of course someone would move to the curb. Even if he couldn't predict everything, he should feel uneasy when running in someone's blind spot, just like I feel uneasy driving through another car's blind spot.
Racing track not in lanes is a messy thing that requires wits. If you really want DQs for every little perceived infraction strictly, you'd have to DQ a significant fraction of the field in every competitive track race ever run. People are cutting each other off right from the start of races getting position. That's just the nature of racing. People trying to get to the same spots, each with limited reaction time, different determination, moving on instinct. Raevyn Rogers admits that she isn't that aware of how she ends up where she is in an 800, she gets bounce around so much. That goes for half the field. It's messy, but more exciting than racing in lanes.
You know what runners say about finishes. Don't look back. Krop didn't look back.