Op, what’s unsaid here is that there’s planning and enough required knowledge that is a barrier to entry for most people.

Planning: the engine will only get hot enough to do this after a drive of 30-45+ minutes, plus cook time. So for each person, each trip, it means specific planning of what to make, and when you can make it.

Knowledge: engines vary in design, and people vary in their comfort in how much they trust themselves to do things in their engine bay without risking damage. Taking some wire, making a secure spot to hold something wrapped in foil, and it not being in the way of anything AND if it slips or comes lose won’t get caught in a belt is something I feel fine doing, but I do a lot of janky redneck stuff all the time.

Most people barely know how to change their oil, and since the 90s, more and more cars are complex such that they seem designed to be repaired and maintained by someone else not the owner. This makes the simple act of opening the hood intimidating for most people. One survey I found online puts comfort in doing basic cat maintenance at 20% of people. Extrapolate from there an increasingly small group that is comfortable doing weird stuff, ok doing risky weird stuff to their car, and who don’t want to stop at a real restaurant to eat on a road trip (where my spouse will prefer to pee, not the side of the road), and you get a small enough number of people that is not surprising this isn’t common.