Honey traps, basically.
I.e. particular places that attract disproportionate numbers of visitors. This brings litter, parking issues, noise, damage to trees, human and dog excrement etc. I moved 13 years ago to near a series of reservoirs outside of Edinburgh. During and after COVID, it would attract 100+ cars on weekends/ holidays such that locals could not get in or out of their houses due to back to back parking over about a 2 mile stretch of single track road. One person meets another going the opposite way, or parks too far out, that's the road blocked.
Trees were felled for firewood, people camped for weeks at a time, right next to their cars, parties all night you name it. People used to order take aways tontheir tents.
There was another such spot in the Pentland Hills, another I found down in the Borders, several around Loch Lomond and the Trossachs. It got so bad in the national park, in the end the national park authority passed bylaws prohibiting camping entirely outside of designated sites. Which has ruined it for everyone. Local councils can't ever get their act together to do the same.
I believe the NC500 route is not faring any better. Complete poison chalice that one.
The problem is the volume of people in the UK. It ceases to be an effective policy if you share it with 100s or thousands of others in the same place. And out of those people a minority will be inconsiderate choppers, inevitably.
Note England is 5-10 times more densely populated than Scotland. It would be horrendous down here because too many people are stupid and selfish.