What I truly believe is at the heart of this can be linked back to Naomi Osaka, Simone Biles et al and this opting out due to "mental health" movement that has become fashionable in pro sports.
Seriously though - they normalized it and due to a number of social factors super prevalent at the time (race and gender) and everybody bent over backwards to play the violins for these poor athletes who make a ton of money relative to the average citizen for playing sports that they freely choose to (which herein lies the big difference for me between actual mental health issues and sports psychology issues).
So now when things get tough - raised expectations, pressure to perform etc - there is no incentive anymore to tackle it head on and overcome it through strength of conviction. Why? Because with guaranteed $ it's easy to (in the case of Sydney McG 100% because NB do not have reductions clauses in their deals primarily because they "don't want to be like Nike"). And even with Nike, notorious for their hardline contracts with respect to "pay for performance" this also eased off considerably in recent years with the furore around the reductions in contracts for pregnancies (Felix, Montano, Goucher) and that spilled over into deals in general.
Like is it coincidence that we see this more and more since those "pioneers" of this movement got the ball rolling? Even a decade ago the thought of "skipping a worlds" to train for the next season or take a "well earned vacay after a stressful season of 2 races" was simply unthinkable. Mostly because your livelihood was at stake. Not anymore. And don't even start with "that's crazy these guys don't earn that much money" - well really they do if you compare it with the average American household and not the morally disgusting money that NBA players make to bounce a ball and throw it through a steel ring.
Training for next season? Minor knee injury? Don't insult our intelligence - these athletes don't want to run because guess what, track is hard and it's even harder mentally than it is physically. Why do you think all these guys need "higher powers" they convince themselves are out there with individual plans for them, that dictate their performances good or bad?
This is nothing more than running and hiding and taking full advantage of the current system to do so.