To be honest, the destruction outside of the terrorist hunt mode (since the AI is allowed to barricade everything) wasn't really that necessary in the slightest and more "because I want to enter the room through this wall taco" that occasionally gave you a slight tactical advantage of avoiding the existing doorway chokepoints.
Really, the wall penetration did more to determine the outcomes of matches than 90% of the other destruction I caused in the beta. And that's the same as in Call of Duty. Only in Siege, like nearly every wall allowed penetration damage. I think I killed a low health guy through concrete. (May have been a bug tho.)
The few examples in the maps that I'd call borderline key were the places where you could blow through two interior walls back to back and completely avoid hallways (and thus barbed wire, IEDs, cameras, etc.) and come in from almost behind the defenders. I felt those instances were drastically altering the structure of the whole map (or at least that floor of the building) rather than opening a new entrance into the same rooms. And that would be a thing down the road where veterans would start to spend some of their reinforcement to prevent it and force you into the hallway.
The reason the lack of "roofplay" stands out to me is that I believe it's considered a fairly ideal way to clear a building in these situations and that most services prefer to enter a building that way if they can.
EDIT: I guess they don't want to give you an "always free" entrance, and they can't let the defenders get on the roof and not just snipe you before you get close to the building from the spawn points. So that's why they haven't implemented it.
Or maybe it's just like 90% of video games and thinking vertically just never comes into the design process too much.