Perhaps this question is a bit rhetorical and overly answered but here goes anyway.
Why is it that one track athlete can run multiple, close-to PBs on any given day, plus other races. For example in one day, open 400, 4 x 400 leg and 4 x 100 leg two days in a row. Compared to another track athlete who runs only an open PB 800 on Friday and an 800 leg of the distance medley and can’t come close to a PB.
The biggest reason I hear is the athlete “has no heart” or “not in shape”. This seems like the easy answer as there is no thought involved and doesn’t require much analytical thinking to come to this conclusion.
Training non-specific to racing demands. Multiple events.
I know the answer or answers are in the question. Maybe all this rain in the the East has given me a brain cramp.