And because it own them on behalf of the British People, access to a large number of it's portfolio is free and open to all.
One of the properties near me used to have a policy of pay to go in house & any formal gardens, but free to walk on farmland or woods and access to shop and cafe (where obviously you would be paying for stuff), so that everyone could afford to use part of the property for leisure or to buy gifts, snacks etc.
Last time I went that free acces was in the bin as the car park was now charging £5 per car even if you only stopped for 10 minutes. Bus fares to the area would wipe out low paid family access.
Other than commons and footpaths, I can see it creeping towards only being accessible to the reasonably well off - given the increasing poverty rate in the UK that means lots of people are becoming excluded from 'on behalf of the British people'. Dont misunderstand me, I am a big fan of most aspects of the NT but some of their moves are worrying. Last time I went I tried to pay cash for entry and they made such a fuss about 'we have to get someone who can handle cash' it was ridiculous. I was made to feel anyone without a bank or credit card on them was 'not our sort of customer'. Completely bizarre and not very nice.
What exactly do you mean by manage, though? In the case of historic building I can understand that, but an extensive countryside property?
I guess you perhaps come from a town or city? All countryside is managed, even heaths and commons. How to graze the area and what animal to use has lots of knock on effects on wildlife and wild plants. There will also be conservation schemes to encourage the development of some sorts of wildlife and to discourage other sorts, again same with plants.
Farmed areas become even more complex as there are issues of style - modern commercial or organic practices? Rare breeds or commercial animals? Which tenants to let to for farms and for simple housing stock, which properties should be for holiday homes? The impact of NT choices on the local farming community? How farming techniques might impact on local water purity and on the water table for the area, how much fertilizers, what sort and when.
Farming is very complex, its not just some bloke out with a scythe hacking at a bit of self seeded grass. When you see a factory building, you do not assume all the staff, buildings and equipment just sort of appear at random and require no intervention or maintenance or organising - well its the same with a field and related animals, buildings and staff.