What is he supposed to use for money during this escape to Canada or Mexico? Surely he knew he'd be recognized quickly (especially in Mexico). This is not a street smart young man. He has never lived outside his parents' house (IMO) except to travel with Gabby, who supervises the plans. I believe he values his own life (and comfort) a great deal. He needed his parents more than anything, considering what he had just done (left Gabby near Spread Creek, WY). I wonder what he told his parents about why he was coming home without her. Did they ever try to call her? I bet not. They knew he had her phone. IMO.
I wonder if he even knows how to use a map. Whether he could find a border crossing (you should see my students - all of them young adults in a state university. - struggle to locate the borders in between states and transfer those to a paper map). Half of them have been to Mexico within the past 2 years but cannot say which freeways go there, and some take SO long to figure it out in the lab - they rely on their groups to help them out. They're not even clear on what kinds of symbols and lines/shading that Google maps uses to show them boundaries. Some cannot draw a rough outline of California without a map in front of them.
Nearly everyone knows that you head to Tijuana - but they can't name the other crossing. They also know there's a wait and a check point at Tijuana (most of them). They also know it's "south" of where they live - but they do not have a strong concept of how long the drive is. This semester, only ⅓ knew which state lies directly north of CA.
Anyway, Brian wouldn't want to get caught by digital evidence later googling "what's the fastest way to Mexico?" Would he? Even if he can't use a map, he seems aware of general rules of law and order.