Accumulating the assets to buy your own freedom required the permission of your owner, which he could rescind at any time.
And once freed, you were in constant need of a white person to vouch for your freedom. You were in constant danger of being enslaved again, whether by roving gangs of slave traders or by explicit written government policies telling free blacks to leave certain areas or be enslaved again. At any time a white person could whip you and you couldn't do anything about it even if you were free. You would just hope that other white people would punish and discourage that person from whipping you again. No matter what skills you acquired, white people would avoid doing business with you and underpay you when they did.
This freedom was very much on paper only.
Freedom came during the Civil war.

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