Just because a gene has become popular in a population doesn't necessarily mean it provides an evolutionary advantage. It can also be genetic hitchhiking, where a non-advantageous gene tags along with an advantageous one because they're located close together. Or even just genetic drift, where a gene becomes popular due to random chance.

There could be an advantage for this trait, but there doesn't need to be.

Well, I ain't no animal scientist but most fur patterns that I'm aware of exist to either make the animal blend in (by being the same color as stuff around them) or to break up their form so it's harder to recognize from a distance, and I can see how being literally cut in half color wise could help break up their shape

Again that's just a guess on my part tho