Chemical sunscreen famously kills coral.

Some dermatologists have noted that sunscreen is little used in Africa. [1]

I’m not saying that is the only explanation for the reef’s preservation, but it’s likely a significant contributing factor.

[1] https://theconversation.com/sunscreen-wouldnt-have-saved-bob...

That and being 175 feet below the surface. You’re not getting “sunscreen” on mesophotic coral.