Console verification is an important part of ensuring TASes are accurate. For that, we need an interface into the console's controls among other things.
I know its not the legit real controller, but buttons are buttons (analog or digital). As long as you don't mod the console itself, that should be fine for the TAS community, no?
I believe the main issue is that it's very easy to electrically simulate button presses and be confident that the rest of the system is functioning correctly. Once you start simulating the entire controller and its protocol for communicating with the console, you start to enter a realm where it may be possible to trigger inputs that are not physically possible with the actual controller hardware.