There is a modern disconnect among many people as to what they are really seeing in games. I have seen people —possibly even modders— be astonished at the graphics quality of 80's titles like Cobra Command, Dragon's Lair, and the like; shocked because of their modern assumptions about what they are seeing. There is often no perceived distinction between 3D and 2D, other than —erroneously that 3D is 'first person', and 2D isn't.
Both of these games are entirely 2D; cobra command is a rail-shooter in the strictest sense. Its gameplay is very close to
Missile Command; literally just moving the target reticule to aim, and occasionally using the joystick to indicate a singular choice of motion when called for. The flight path is unchanging except for death animations. Dragon's Lair is essentially the same, properly timed input keeps the composite movie playing; mistakes result in death animations.
In the case of Fallout, Tim Cain has said that they (briefly) considered polygonal 3D for Fallout, but that they could not get the performance they wanted from the target hardware, so they went with 2D sprites. That meant that even though they did the work in 3D and with 16-bit color, (the talking heads, the character bodies, guns, equipment, and the backgrounds), they then rendered all of this work as color reduced sprite sheets for use in the game.
Creating new sprite sheets is labor intensive—presumably even
with the original 3D assets, which nobody seems to still have; making them without is a nightmare... but still doable.
There are programs that can be used to speed up modification of the sprite sheets (like Dragonbones), but it might be faster to recreate the 3D asset to generate new sheets, and/or replace the originals.