Speculation only, I wonder how much there was a perverse incentive to continue on the trail *because* they realized that Oski and Miju, or both, were suffering - and EC/JG couldn’t wrap their minds around that (or the attendant guilt) in a rational way. It’s not unfathomable as it’s human nature to avoid, avoid, avoid and “throw good money after bad” when things get scary.
Forgive the dime-store psychology, but our minds protect us against the unthinkable through myriad “irrational” mechanisms. E.g., if they realized that they would likely be charged with child endangerment or animal cruelty after turning around at the river and returning to the truck and rushing to a hospital/vet, they might have minimized the danger (Miju is just tired or cranky / Oski is just hungry….) and continued on.
I am not suggesting in any way that they intended to harm their precious baby or dog - quite the opposite, i.e., the realization that they had inadvertently harmed their dependents was unthinkable/unbearable and drove additional bad decision-making, rather than prompting rational, corrective behavior.