[stonogo]

Being precise about these things gets difficult; arguably some Arab states are still practicing slavery, but with a veneer of indentured servitude. However, I'd like to point out that the Barbary pirates were not Arabs, and the Trans-Saharan slave trade article you reference covers a similarly vast time scale; if we look at the era during which transatlantic slavery markets operated the scale was at least one, possibly two orders of magnitude larger than Arabian imports of slave labor.

Nevertheless, "slow indeed" is correct, and the Zanj rebellion didn't have much of an effect on North African slave trading.

However, the original question was why Arabian slavery was not as economically potent for Arabs as transatlantic slavery was for European colonies. The answer I'm trying to give is twofold: 1: it was, just vastly earlier than European colonialism, and 2: by the time the transatlantic slave market was established, the Zanj rebellion and other events had had a deleterious effect on slaveowning culture in Arabia. The question as phrased assumes everyone was getting rich from slavery at the same time, which is not the case.