They decided to go with the design decision of having the turrent control via mouse...
I imagine the main reason for this was simply to avoid people having to switch between movement (WSAD) and head control (Mouse) and movement (WSAD) and turret control (↑↓←→), or whatever combination of the 2. Having the turrent controlled by the keys as well as giving commands to the tank crew would be a little awkward.
If you really want the turret control to be done with keys (if it isn't in the game) then get a free mouse emulator and bind it the keys you want to use.
I feel that in all honesty, using WASD for turret movement and the mouse for head movement was the most intuitive and versatile control scheme. I could, for example, turn my turret towards a choke point while looking behind me to check whether or not my supporting infantrymen were moving up. I could aim my main gun at an adjacent oblivious enemy tank while calculating the range to its more distant partner using the binoculars. It felt natural--the simple, quick control to simulate turning my head, and the mouse keys to move the bulky turret.
The current plan for RO2 is for the commander, who no longer guns, to use the mouse to look around, clicking to order the gunner to traverse the turret while using WASD to direct the driver.
What everybody is concerned about, however, is not what the commander is doing but what controls the gunner must use to traverse. In his case, since he is the one actually manipulating the turret controls, and since he does not need to worry about the tank's movement, using WASD is the most immersive, historically accurate option and sacrifices nothing in terms of gameplay. Will this be confusing? Disorientating? Unfriendly to newcomers? Well, when I first tanked in RO:O, I moved the mouse, found it wasn't moving the turret, then tried the WASD keys and found they worked. That oh-so-high learning curve? Elapsed time: 5 seconds.
The main problem most new players have seems to be learning to open the hatch and look outside the tank.
Besides, remember that RO2, unlike Ostfront, will feature tutorials. New players will figure out the system quite easily. And tanking is supposed to be more complex than running around with a rifle. Of course it will take longer to master.