There are Three main branches of VR game development
1) Cockpit games
These are fine. Cockpit games do well with a controller, especially when head tracking and aiming are separated such as in battlezone
2) Third Person Games
These are an interesting little aside popular on the rift. These do not suffer as you are watching a character that you are then controlling.
3) First Person Games
These are where this mandate sucks. With motion controllers being your only input you build up a game where you shift aiming and interacting based on proximity of the controllers independently in each hand. Once you require making these games support a regular controller you bring into the equation many things that a dev shouldn't have to think about. How do you aim, Right analog stick? Well thats way slower than a motion controller and aims differently. Oh our bow now needs a reticule. Oh now we cant use a two handed usage with the bow. Oh shit now that we are using the stick the game is too difficult as the user cant react fast enough. Ok what if we changed it so they aim by turning their head. Awe shit now its too jarring in frantic combat and users are getting neck soreness. Ok aim with the light bar on the controller. Shit now they are loosing tracking whenever the user twists the controller outside of the view of the camera. Ok we can start guesstimating their aiming with the gyro once the camera loses it but ah shit that is too inaccurate for VR.
And this is only one small example of game development questions that supporting a standard controller gets in the way of for example 3. There are countless other differences that would need to be accounted for.
A developer making a game that falls into category 3 should never be REQUIRED to support a standard controller as it will cause their design to suffer depending on the goals of the game.
No the point is you can develop games that require both hands tracked you just have to provide an alternate control scheme for DS4. Again, its all about consumer choice and uniformity since all PS4 has a motion tracked controller included.
The problem is that game design for some of these games WILL SUFFER as a consequence. Developers should have the choice to not support the DS4 if it doesnt make sense for their game