At first glance this decision somewhat blows your mind and reeks of stupidity but theres a reason behind it. A very stupid reasoning built on nothing but corporate greed but its a reasoning nonetheless. Sony isnt allowing the functionality of MP3 files or audio discs simply because they want users to sign up for their music streaming plan. Yes, this also means you have no way of utilizing custom soundtracks for PS4 games, and thats a pretty deflating blunder in certain cases. Ripping away options isnt exactly the right way to approach something like this though; something Sony seems to now understand as the guide mentions that the architectural team is looking into reversing this decision.