Look it's not a surprise that phenoms just can't sustain things and it's more mental than physical. You go from racing immature physically inferior talent to a collection of future Olympians from various national programs, in college.
It's well hard for them and maybe they over-train and get fatigued . Pretty soon they start wondering if it's all worth it....
Most of these kids are academic oriented and want a social life as well, so there's that.[/quote]
As noted, no, it's not more mental than physical. If anything, females blow their male counterparts away when it comes to mental 'toughness'. The more mentally grueling the race, the better adjusted performance by females.