Lol wat ? 2D is way more cheapjer than 3d. You are all trolled by japanese fighting games developers.
Cost of making fallout1 was3mln dollars and back then and 2D 256colour was super high tec.
Drawing/rendering a billion different sprites for every different set of armor for both genders for any number of races for any number of customizable looks, for 4-8 directions. And all of those need frames for idling, walking, running, punching, kicking, stabbing, swinging, shooting...
Oh wait, someone just said "wouldn't it be cool if we had grenades?" time to make another 800 sprites for "throwing"
OR using the magical power of 3D acceleration, make
one skeleton that does all of those animations which you only need to rig up once because it can rotate in realtime and attach an infinite amount of skins onto it.