How come Thomas Jefferson did not release all his slaves?

He wanted to but was in so much debt from importing rich European food that he couldn't afford it. Slaves were property and were therefore worth money; if he released them, he would be giving away what wasn't his to give away [not his money]. Also, he thought it was cruel to release them to the streets as they had become dependent on him. Some say he planned to sign the freedom papers before his death, but he died too quickly.