Here the central and local governments have been slowly restricting the rights of people to camp. This is because the Freedom Campers, as they're called, generally don't respect the places that they're staying - destroying the environment and leaving rubbish and human waste behind.
Sometimes when people go to another country they don't behave like guests should and it's the sad case of a few ruining it for everyone else.
Scotland also has a fantastic network of "bothies" which are houses in wildnerness areas that are free for anyone to stay in as long as you act sensibly, which most people do:
The sad thing is they're looking to reduce them because some of them are quite old and the cost of maintenance is high and 1,000 odd buildings which are in very remote locations are no doubt a PITA to manage.
But people are constantly getting caught in the wilderness by a sudden change of weather and the hut network saves lives.
Some of the abandoned ones have been adopted. You might appreciate this: http://remotehuts.co.nz/
As far as I can tell doc seems to be engaging in more commercial activity, buying remote properties that are cheap (because they're remote), and renting them out Airbnb-style. My guess is they may actually make money from this activity. And they may need to because of years of reduction in government funding, in real terms. You may know more about this than I do.
You can still camp anywhere on DOC land, which is about 30% of New Zealand.