It's just another "trash-sport" pseudo competition. The fact it's silly enough that the US is primarily represented by people who retired from alpine racing doesn't matter to the broadcasters. It's televised for the same reason that "Celebrity Apprentice" is: people who know nothing about sports (or business, as the case may be) find it entertaining, because it does not require that you know anything about the sport (or business) - indeed, it encourages lack of knowledge.
The primary benefit of ski cross is that it provides a practical demonstration that boarder cross is even more silly.
Aerials has about as much to do with skiing as diving does with swimming.
Moguls is basically a contest to see who can do a bizarrely regimented and highly specialized mini-task over and over really fast.
As for half-pipe boarding, I like the fact they always describe their spins in degrees ... a 1260 sounds like a ton of spinning, even though a figure skater does the same thing every time he (or she) does a triple axel: and without being tossed in the air by an engineered jump. It's around for the same reason death metal bands are. It allows the youthful spectator to feel he is way gnarly ... plus, the US wins most of the medals since the rest of the world is apparently less needful of feeling way gnarly, and they haven't gotten around to bringing in half-pipe skiers to provide a practical demonstration of how silly it is.