I remember asking Dr Evenson a lot of questions about the why's and how's, and he confirmed that the most probable reason he sees is the man's age Since there is nothing you can do about age they then go over all other possible scenarios just in case it is something else. Weight is an issue too, people are fatter than ever and it does not help generate good sperm (don't remember exactly why, possibly body heat cooking sperm like in a hot tub). But yeah, age was the biggie above all else. Doesn't mean an older man can't have great sperm though, but if past 42 or so, at least test and find out.
My other line of questioning was, so what if someone's index comes back at 50% fragmentation, doesn't that mean 50% are still theoretically good? Answer was no, after it hits 30% fragmentation, live birth was very unlikely. He doesn't know why 30% is the threshold but he went into a longwinded explanation about how they have crunched the numbers for years and keep getting the 29-30% limit for a live birth. Best thing is to try to improve numbers before a cycle. He kept citing study after study (much like Dr Check actually) and a lot of his work is for animal breeders...and IVF for cattle & horses! Breeders use the test to determine when the prize bull gets put out to pasture (cringe).
To answer your question from below, sperm banks will have donors screened upon request. But since the overwhelming factor in fragmented sperm is age, sperm donors are generally young and healthy, and are 'proven' with having a recent live birth or 25 there isn't much demand. I don't remember the age cutoff for sperm donors at banks but it is under 40.