OpenGL is a good way to improve the performance of the game by directing the game demands to the hardware.
But Doom is natively rendered by software, which makes this way to render more secure.
I'm not saying OpenGL is bad. In it, we have dynamic lights, 3D platforms, gloom and other good features. Not to mention the texture filters, alpha lights effects, excellent and colored fog effects.
So why are we leaving the OpenGL? We're doing this because we want a game with no limitations for the players. Do they have the correct graphics drivers? No problem, they can play. Do they understand the bugs that often occur in an OpenGL based game? No need to...
Ok, we have pixelated graphics? Yes, but they are sharp as the good classics games!
Set your resolution and have fun! No vertex problems and stuff.