So it's part of the cost. Most people travelling long distance fly and rent a car at the far end.

Would you pay an extra $500 a month to avoid having to spend $1000 renting a car twice a year? Probably not, so the question is how much more does it cost to not rent the long distance car.

And I've never rented a car where a 1mm scratch would require fixing, nor a 1cm scratch

You're lucky, I have, several times in Germany, where some dealers come with a ruler measuring them, plus km limits per day.

Enterprise's guidelines is

    Bumper Damage IS: Dent/scratch larger than 6” (size of the damage evaluator), or hole/tear of any size

    Exterior Body Damage (Non-Bumper) IS: dent/scratch larger than 2” circle, or hole/tear of any size

    Glass Damage IS: Any ‘Star’/crack

I suspect companies like Europcar, Hertz etc would be similar.

Even that, in term in term of cost it's not much. And what's the likelyhood of scratching the car? (It never happened to me with rentals)