Or maybe the pressure of competing at that level and having to maintain it for a year longer than she planned just got to her.
That could very well be true. The stress and pressure of the competition could have been the trigger that finally set her off.
Her recent explanation is that she experienced a disassociation disorder that gymnasts call the “twisties.”
https://www.cbsnews.com/news/simone-biles-opens-up-withdrawal-tokyo-olympics-twisties-instagram/
In 2018 she discussed having an episode:
https://ftw.usatoday.com/2018/07/simone-biles-comeback
So this does check out. If this is the case then I misspoke and should not have labeled her a quitter. But why have we not heard this happening to other gymnasts during top-level competitions?