Local conditions
Fence lines are where the recurring cost sits. Trees along a boundary drop limbs onto the wires season after season, and each drop means a repair, a section of ring lock replaced, and stock potentially through the gap before anyone notices. Clearing the trees that keep causing it is cheaper over a few years than repairing the fence repeatedly.
Paddock trees carry their own issues. Grown in the open with no competition, they develop wide, heavy, spreading crowns, and when a union on one of those long horizontal limbs fails, the limb that comes down is far heavier than the tree's height suggests. Stock sheltering underneath compacts the soil over the root zone as well, which slowly reduces tree health.
Access is the third thing. Gateways narrow as vegetation grows in, tracks get overhung until machinery cannot pass, and a single failure across the wrong track can cut the property in half for the duration. None of that is urgent until the day it is.