In a 5,000, the person who pushes the 4th Kilometer (and before) close to all out invariably serves as a sacrificial lamb and loses. That is unless they are hugely better than the field. It is too grueling an event with margins too thin for an athlete to win crushing the pace like that.
The last athlete capable of it was the GOAT Kenenisa Bekele. He did it in 2008 running 12:57 (7:35 last 3K, 4:57 last 2000, 2:25 last K). The field then was not at this year's level with Eliud Kipchoge (12:50s shape), Edwin Soi (12:55 shape), and then a few 13-flat type guys. Bekele was in world record shape and at the peak of his powers (8:04i, 26:25 10K, 10 second victory at the Golden League Final).
Good as Cheptegei is, he is at most 5-15 seconds better in a time trial than a large group including Jakob, Kimeli, Krop, Barega, Kejelcha, Grant, Mo Ahmed and go on down the line. So no one athlete is going to do it alone. After Oscar Chelimo won the heat, there's no way they could ask him to be a sacrificial lamb. The Kenyan coaches might have ideas of pushing it faster, but Krop knew that the race was shaping up well for him given that he has great speed. A fast pace benefitted Kimeli, but he knew pushing it near his limit would just mean he'd have no kick. He opted to run reasonably slow but not down to a crawl. Ebenyo should be * that * guy to take the fall, but he was unwilling to sacrifice himself. The Ethiopians can't ask Edris to sacrifice himself, given that a crawling pace might give him a chance and his pedigree. Barega had reason to believe a slower pace might be good for him, but this was just a disastrous Champs for him. Kejelcha was thus pretty much alone, and he has never been able to kick well after pushing the pace. So, the game theory and calculus really didn't work well for anyone.