The only way to improve 2d stuff is redrawing it. So 2d games can only be remade, not remastered.
2D stuff can absolutely be improved with no redrawing. Take a look at Smash Melee running on Dolphin. Nobody redrew those models.
Also, remaster does not strictly refer to visuals. You can leave the visuals entirely alone and rebalance the gameplay, fix bugs, change the audio up, or otherwise improve a game while leaving the original source code mainly in tact.
Absolutely right. You can improve 2D art without redrawing.
Some art can scale indefinitely upwards. I.E. Vectorization.
Otherwise simple upscaling with various de-noising, sharpening etc' algorithms can enhance an image significantly.
A.I upscaling is a thing these days as well, which leverages neural networks... It's used rather extensively in the PC modding community at the moment to give a new lease of life for old 2D game textures.
For example here is one from morrowind:
Oh, no wonder I'm bad at Melee. Apparently there's a 3rd dimension I never realized I could travel into. How do I do that?
Remaking art assets for 2D clearly meant 2D graphics. All Smash games had always 3D graphics, even though they have 2D gameplay. And with 3D you have uch more option for scaling it for different reolution by tech, without redoing anything.
Smash uses allot of 2D sprites/assets.
Textures tend to be 2D images anyway, laid on top of a 3D model.