There are answers to that in criminology and psychiatry, but we are not allowed to mental health here. However, we all know there's a flight or fight response, right? Well, it has to do with that. We also aren't to give personal anecdotes, but trust me, I know a particular person (for almost 50 years) who has really had to work on his tendency to flee when highly stressed.
Some people...flee...or avoid...or "distance"...or go down into autopilot. There are biological substrates to this. The "autopilot" can be seen on MRI, actually (if you're lucky enough to get a person willing to go inside one while in that state...it involves a sort of disconnect between parts of the brain that normally light up altogether in emergency situations - but not always, some of us sort of fall apart...one technical word is "decompensation"; I can provide search terms for scholar.google if you DM).
IOW, I think BL was IMO terrified and completely alone and out of his depth - he had been away from his parents on only two different occasions we know about.
First trip was a bit less planned (Summer 2020). This one was a working trip - where perhaps both of them were hoping to monetize their Van Life (I think it's clear that they were working on that - an added stressor). In theory, Van Life people either work gig or minimum wage economy when they need money (finding the right free places to camp - it's estimate there are over 1000 young people in free camping near Moab, waiting tables, working in grocery stores, McDonald's). Others do manage to make enough money off their youtube to fund their Van Life.
My SO and I can unlock each others' phones with our faces - nearly everyone I know in a relationship who has an iPhone does it. Gabby is clearly controlling her own phone in several videos she makes while Brian is out hiking. Brian actually left her alone for about 5 days, during which time she could have broken up permanently with him, started driving her van back (slowly, if it was a challenge), and she certainly used her phone according to her father. She also had a hotel room that would have had a land line.
She has her phone next to her while making meals, while doing so many. things on the trip - Brian is no where to be seen in those videos.
I don't think it helps to treat all DV situations as so much alike - each situation is very different. If in fact, Gabby could not use her own phone, then why is she sitting in the back of the squad car using it while LE talks to Brian? Why does the Ranger tell her to go back to her conversation (I believe the ranger thinks Gabby is talking to her mother - but that's not confirmed).
