Freeze and fawn (compliance/cooperation/appeasement/submission) responses are far more common than flee or fight responses, evolutionarily and across species, not just humans. It used to be less risky to stay still in case a predator lost interest/didn't notice you on the first place, or try to cooperate/comply rather than risk predation drive by running or damage by fighting. In complex situations or prolonged circumstances you're likely to get a mix of all the behaviors.

This is a good overview on what happens among sexual assault victims+survivors from a neurobiology point of view. It's a 2 hr lecture for first responders and helps dispell a lot of harmful myths like there only being "fight or flight" responses, and how memories don't form in the same way/a person's composure may seem despite going through trauma.

https://youtube.com/watch?v=dwTQ_U3p5Wc

And for any survivors seeking additional resources or exercises on navigating common trauma responses, this is a useful diy guide: https://www.thehavens.org.uk/media/Self-Help-Guide-for-Survivors-of-Sexual-Assault-v.2-March-2019.pdf

Both are useful to share with others also to spare survivors the effort of having to educate people about why they're behaving / experiencing whatever they're going through.