Because people really don’t do this “all the time” and especially not when they’ve got no history of any kind of instability. She has a job that she’s had at least a year (or close to it), she’s enrolled in school, she has an apartment, she has a pet, she has a car, she isn’t known to have a drug problem, she seemed to have plenty of friends in her life.
She contacted her mother and said she had made it to SLC safely, she contacted Lyft for a ride, then met an unknown person in a park at 3 am and hasn’t been seen or heard from since. How can you not find that unusual?