No piece of land is the same
Land is a unique commodity
Land is expensive
A person who enjoys specific right over a land refuse to let the rights lose due to the change in the ownership of the land.
If the right is lost, land could loss the market value.
For instance, in the case of land locked land with a right to access the land via another land owned by another.
The purchaser may be interested to invest in the land if there is an assurance that the route to access the land via another land could be exercised by him regardless of any changes to the ownership of the land over which it is exercised.
Without any assurance, the future owner of the land may deny access to the land locked land via his / her land.
As a result the land locked lose it market value.