Historically, Jefferson wanted to abolish slavery in the Declaration of Independence but was not approved, so why'd he keep his own slaves?

In April 1820 Jefferson wrote to John Holmes concerning slavery:

“ there is not a man on earth who would sacrifice more than I would, to relieve us from this heavy reproach [slavery] ... we have the wolf by the ear, and we can neither hold him, nor safely let him go. Justice is in one scale, and self-preservation in the other."

Jefferson characterized slavery as a dangerous animal (the wolf) that could not be contained or freed. He believed that attempts to end slavery would lead to violence.

Jefferson believed the only way to emancipate slaves was to resettle them outside of the United States.

Economics.

He was a cash crop farmer and that takes labor.

Why did you start your question with the meaningless word "Historically"?

Jefferson added a paragraph to the Declaration of Independence criticizing King George and slavery.

" He has waged cruel war against human nature itself, violating its most sacred rights of life and liberty in the persons of a distant people who never offended him, captivating & carrying them into slavery in another hemisphere or to incur miserable death in their transportation thither. "

Some of the Southern colonies objected and the lines were deleted.

Wrong, none of the Founding Fathers wanted to abolish slavery cause they were all rich and slave owners, George Washington himself owned a thousand slaves, before and after the American Revolution, the Founding Fathers just wanted the Colonies to become independent from the tyranny of the British Monarchy.

"Give me liberty or give me death" that meant freedom from the British Empire. A quote said by Patrick Henry but usually attributed to Jefferson.

The Constitution was written for those who weren't slaves, actually many articles of the Constitution started with the phrase "Every free man..."