As I understand it, the council own the land and Haydn Green Trust have a 150 year lease who then sublet to the club. the club owning the infrastructure (stands etc)
It was set up this way to ensure the club has a home "forever". The rent is like ยฃ20k a year (depending on which league we are in) so nothing that will significantly improve the clubs revenue if they did own it.
Personally I would prefer it to stay this way, we have fantastic owners now but removing the land as an asset deters greedy/selfish owners selling the land to make a ยฃ.
Securing a permanent training ground is far more important.