Help me understand Shaco's rework...

Why was he reworked from being mostly AD based (but able to be built AP as well, let's say he was balanced 50/50) to being mostly AP based? Why does he have absolutely trash passive (saying you'll build crit Shaco)? Why does he have so low base damage, but built to scale so insanely into AP? Why does he have such high mana cost at such low base damage abilities?

I didn't play the old Shaco much, and we have no idea how he'd perform in the new jungle, but I played the new one in jungle and I loved it, but every time I end up with him on other lane, I feel handicapped compared to other champions...