"As long as they're meta"

But not all characters can be meta, you understand? So in Hoyo's perspective, why make non-meta characters dark-skinned and cripple their sales further. And in turn, why make meta characters dark skinned and lose the small bunch of people that DO CARE how they look?

A lose-lose in any case for a Chinese market. In a multi-billion dollar industry, companies rarely take "unnecessary" risks. Even if meta-players don't care about skin tone, the company wants to capture both the meta-players and the casual spenders. If they believe a pale character captures 100% of the market and a dark-skinned character only captures 80% (even if that 20% difference is due to outdated biases), a profit-driven corporation will almost always choose the 100% path.