Not all land is a good pasture. In many parts of the world, good pasture are also efficient carbon sinks. In my part of the world those carbon sinks are rare (only about 10% of pastures are carbon sinks), and the few that are good are even better as farmland.

That overlap is not 100%. Some good pasture is bad farmland, but the claim that good pasture is good farmland is a good rule of thumb