Wow, the level of neurosis shown by some over a metal box... Well, I suppose if they've got nothing better to invest time, effort and money in, then it's relatively harmless.
However, unlike most other interests and hobbies, it doesn't seem to make them happy, and instead promotes stress and anxiety. Why do that to yourself? It's not a freshly restored E-Type or Dino that needs curating for future generations, it's a mass produced appliance.
The financial argument is rubbish - the scrap man or insurance payout doesn't care about how spotless clean the car is as the end of the day, nor is a trade in price significantly different, certainly not worth the time and effort expended (which can instantly be written off by a ding in the carpark).
For the vast majority with real lives, they have far more important things to spend their time enjoying.
Plus most lives aren't remotely conducive to spotless cars - consider children - a reality for the majority at some point. First (well not exactly first, but the very first doesn't always result in bodily fluids in the car) comes morning sickness, so plenty of vomit. Then waters break (we managed towels on seat, but not 100% protection). Then the real fun - a baby capable of producing near limitless quantities of wee, poo and vomit at high pressure. Then there's the milk that jets out in every direction, again at high pressure. That's before they start eating and drinking on their own, plus the mud, pushchair, bikes, random sticks, snails, stones etc. How does a 3 year old get into a car seat without climbing on the sills and seat? The vast majority of the above applies similarly to dogs...
In summary, don't buy our ID.3, but to be fair, the exterior is pretty good despite various diversions into hedges (it's either that or losing a wing mirror to a white van or the entire car to a tractor) and it being washed maybe 4 times in as many years...