The idea behind this was that if it was found to be easier to get a commission in one of the cadets forces, they wanted to avoid people going into the ATC (for example) to get commissioned and then moving straight over to the ACF. The expectations of what the organisations want and their interview processes are so different.
Because it’s not the same commission anymore than an RAF commission is the same as a Land Forces commission despite both being military. An ACF and ATC commission are both Cadet Forces commission’s in terms of type but you are commissioned into one of the cadet forces, not all of them