Its just preference. Guys like Dennis Chambers had his up high, and some top rock guys in the 80's. People see that and immitate that, and its what they become used to. Its more efficient to have them lower though....
I'll say this as well. When I was a kid taking lessons, the cymbals wer enot high, but to me they seemed high. then you grow, and you are used to cymbals being high, so you either adjust, or keep raising them. I was looking for more efficiencies, so I kept them lower.