Early versions of facial recognition had difficulty working with darker skin due to genuine technical challenges, namely lower contrast between facial features and the background skin color (e.g. dark eyebrows on dark skin vs. dark eyebrows on light skin). This was not solved by hiring dark skinned engineers, it wad solved by a different technical solution: infrared cameras that could better sense features regardless of skin color for example.

The developers of facial recognition tools were aware of the early devices' limitations, and dedicating resources towards an approach that worked better on subsequent iterations. Why people think things would have automagically worked on the first iteration if the teams building the devices were more diverse, and why people continue to use this as an example of the necessity of diverse teams is a mystery to me.