The human brain was not designed for a task which requires hours of siting down doing mostly nothing while being hyperfocused the entire time ready to take over in an instant on the rare occasion something happens. While running or cycling your brain is actively engaged keeping yourself upright and avoiding obstacles which keeps you alert.

That's true. Humans are bad at this task. On the railways they have a problem with this too, "Lookout" seems like a ludicrously easy job, but it's basically impossible because you must pay attention to an incredibly boring thing for hours or your friends might die. Getting rid of human lookouts should be a priority but it feels easy and so it's hard to motivate this.

Seems at least somewhat comparable to walking through a forest full of predators, while, say, hunting/gathering.

Evidence that is is compatible with our psyche is the fact that we're at 1.19 fatalities per 100 million miles driven, and ~50% of those being booze and/or speeding.