In Chapter Five, why do the owners of the land want the tenant farmers to leave?

The bank wants the land to produce profits, thus, the owners are going to evict the farmers, allow machinery to take over the labor, and lastly, they're going to plant cotton. After the cotton crop kills the land, they plan to sell it.

And at last the owner men came to the point. The tenant system won't work any more. One man on a tractor can take the place of twelve or fourteen families. Pay him a wage and take all the crop. We have to do it. We don't like to do it. But the monster's sick. Something's happened to the monster. But you'll kill the land with cotton. We know. We've got to take cotton quick before the land dies. Then we'll sell the land. Lots of families in the East would like to own a piece of land.