Some games are so borked from a technical perspective they'd need a remake to work right, like Oblivion. That game is so technically bottlenecked by itself that even on modern hardware I fucking stutter, and I've trawled so many performance mods with fellow players in the comments just having to come to terms with the fact that no mod can fix the inherently poor optimization on an engine level.
Remakes can definitely be warranted in certain cases. Sometimes it's easier to just start over clean than try to untangle an existing mess and Frankenstein it back together. Sometimes making vast changes can produce an alternative reality of a game to be enjoyed by more or a different audience, like the Resident Evil Remakes, which are fucking excellent, or the FF7 remake, which, while contentious, is mostly only so because of purists, who do still have the original they can play (and I do believe companies should always keep the original around)