Why do authors Almost Always pick Black haired MLs when the side characters look much better? [The Incognito Princess]

I was reading "The Incognito Princess" (which is similar to "Side Characters Deserve Love Too" BTW), and I realized that the side characters look just as good (if not better) than the ML.

I can't help but wonder why authors mostly prefer a black haired ML. The Art in this series is amazing. One of the Best I've ever seen.

I highly recommend this series.