I think it was a smart switch by Chicago. Their style of race was competing with Berlin, but African runners live closer to Berlin and the course has historically been faster than Chicago. Now they get to compete with New York in a championship-style race. The Chicago course is way faster than New York, so runners like the top Americans can get the slower race at the front, have a better competitive chance, and finish with times more respectable than you see in New York.
I'm not sure it's a coincidence this happens right as Wittenberg steps down, too, as they have to think going forward they can poach the type of talent she was good at recruiting (first time American marathoners).
Realistically this means they lose the time trial record setters unless they can offer huge appearance fees, but they are likely already getting Berlin's sloppy seconds. I'd wager, though, that they are hoping seeing American marathoners finish higher in the rankings will cost less and be more lucrative to their local branding going forward.
It's an undoubtedly weak field. Many top Africans have aged. Those guys could use a win to revitalize their careers, though, so it's a little bit exciting to see them duking it out. The women's side is full of American masters (who I actually look forward to seeing race it). I love that Joan Benoit has the third fastest PR. Florence Kiplagat is the best in the field by far, but I have to wonder what Renato is thinking having her in this race with the pacers removed. Renato, why Chicago at this point? Is it better for Olympics training cycle timing and preparation? Money? Location?