Yeah, it would have been fairly common to have a small number. Even if you didn’t “own” any people, it was possible to “rent” their services for a time, increasing the number of households that directly benefited from the system.

As for why they didn’t just run away, several reasons I know of. One, it was hard to travel incognito, especially as a visible minority.

Two, black people trying to do so in slave states would frequently have been required to keep a “slave pass” on them to travel away from their “homes” at all, and the fact that it was generally illegal to teach enslaved people to read and write would have further complicated the inherent challenges of forging one.

Three, enslavers would take out literal classified ads for “runaways” and offer bounties.

Four, overarching all of this, all slave states had laws regulating the relationship between free people, enslaved people, and the state, and the most organized law enforcement institutions in the antebellum South were the slave patrols.

No society is just one thing, but the Antebellum slave states had a systemic and pervasive infrastructure of laws, customs, and institutions to ensure chattel slavery “worked.”