As I've allready said about Antic's comment, that's an explanation that makes sense to me.
But in the end good-looking is a matter of taste too. A lot of covers posted in this thread are imho an outcome of that mentality that labels/artists want to sell. Like the Spliff It Up cover or the Talamasca cover, boring standart "art"-work not linked too much with psyculture anymore. I'm still a sucker for covers with phantasy and multi-colored stuff.