why not go the other way around and make initiative a d20? i'd like the game to be as faithful as possible to dnd. especially because most changes make literally no sense or remove gameplay depth.
My guess would be that they found D20 initiative rolls to have too big impact on battles, and thought it was easier to balance them with less randomness.
I disagree that this particular change removes depth though. Less randomness allows you to plan ahead and strategize more, while more randomness forces you to react and adapt more. Devs need to strike a balance between the two to make combat fun.
