Answer:
It was hard for sharecroppers to escape the debt cycle because they could not make enough money to pay back their debt to landowners and buy their own land.
The sharecropper is already giving the landowner half of his crop. He can only sell the other half of the crop.
The sharecropper needs to buy all his necessities from the landowner, who usually charged him at sky-high rates. This would have further cut into his cash.
The landowner treated the sharecropper unfairly, charging the sharecropper more than he needs to pay. Until the sharecropper pays off this debt, he needs to keep working, which is why the system is so difficult to overcome.