Lack of footwork, creativity, and experience, and a lack of fundamentals IMO. Martin both look like kind of kids who only ever did layup lines and wonder why they can't finish in the game. You watch Martin and Cole going to the rim and they're both super stiff. When they try to euro-step or create and angle they don't really get anywhere. Neither of them have a counter when a help defender steps up. Gaffney is just too timid despite some explosiveness, shies away from the defender and makes his shots way too difficult. And tbh Adams just isn't very good right now. Great kid... but he has no touch and seems to just make the wrong decision when he gets in the lane.
They also don't use a jumpstop, which Hurley is preaching for a reason (as well as guys like Jay Wright who is RELIGIOUS about two-foot finishes in practice)--it's a bail out option when you aren't able to get your shot up. You can pivot, try to find a new angle, or kick to a shooter. At worst, it's a jump ball or strip TO instead of a monstrous block that gets the other team energized.
Just my 2 cents.