Removing very old stuff might make it easier to change other things that are still used by other drivers. Let’s say that both 3dfx and Geforce FX (2003 cards) call the same functions. Let’s say that the function to display a texture has 2 different sets of code, one to deal with the older 3dfx, another for the geforce. If you no longer need to support the 3dfx, you can also remove the whole set of code it needed, possibly making things slightly faster for the rest, as it’ll no longer have to check for a 3dfx card. You can also add something you couldn’t before, due to the limitations of the “minimal” card expected