"We ask questions where we know the answer, but don't necessarily know why" But that doesn't seem unique to philosophy. E.g. chemists knew that heating water would make it boil, but wanted to know why. It seems common in much research and doesn't seem very counterintuitive afaict.

I think the difference is that to understand why water boils you don't have to entertain the idea that it doesn't. Whereas philosophers have to at least imagine what it would be like if murder wasn't wrong.