Reason why? Nothing prejudicial, just requires separate implementation and they haven't gotten around to it yet.
Time Frame: Usual SoonTM No idea, but it'll be announced.
What skills? - Could be some combo of strength and dexterity or just Dex. I'd see them fitting into NPW rules, as despite being "Thrown" and therefore projectiles, they are not propelled by artificial means like all other Projectile Weapons. See below for quote from Syn in a similar thread in the General Questions forum.
“Thrown weapons are not separately implemented yet. They will be. There are plans.
Currently they use the same equations as any other type of ground combat, except without an associated weapon skill. So you'll have a higher miss rating with thrown weapons due to the lack of hit bonus for associated weapon skill. Strength has absolutely nothing to do with them. The mouseovers/Character Skills rules descriptions for implemented skills are accurate.
They are not consumed on use at this time.
Future implementation will be announced at some point in the distant future. It's not completely worked out yet.