The Nike 'Breaking 2' race was not considered a world record because it violated official rules, specifically by using rotating pacemakers and a new shoe technology with a carbon fiber plate.

“now you can't hire someone to run a sub two hour marathon in order to run a sub two hour marathon so they had to have runners dropping out every couple laps and new runners swapping in that's not allowed according to the rule the official rules of marathoning so that's the main reason that this race that nike had planned was it was not an is not considered a world record because it doesn't obey those rules and then the other the other factor the big factor is they introduced a new uh a whole new type of shoe that had a curved carbon fiber plate embedded in the sole that improves running economy in other words it allows you to burn less energy to sustain a given pace by about four percent on average”