"The contracts stated that OpenAI would pay an hourly rate of $12.50 to Sama for the work, which was between six and nine times the amount Sama employees on the project were taking home per hour."
OpenAI paid $12 an hour, it's Sama that paid them $2 an hour. People should be upset at Sama, not OpenAI. I'm sure you could find Americans willing to label data for $12 an hour.
From OpenAI's perspective, they likely thought they were doing good by going with Sama, since Sama's mission is to provide work to people in Africa. From their website: "Since our founding, we’ve pioneered new technologies and business methods that harness the power of markets for social good, meaningfully improving employment and income outcomes for those with the greatest barriers to formal work."
This is a story about Sama exploiting cheap labor in Africa, if that's what you want to call it, rather than OpenAI specifically aiming to do that.