Why is Cameron doing this to his movies?

They're not tech people, they're theater people. And they're easily wowed by the big new fancy-smancy tech that is "cutting edge"
We've seen this before, with George Lucas' special edition Star Wars and the prequels being full of the finest CGI 1999 could offer. It'll probably be a decade or two before this stuff is anywhere close to looking decent.
- Legit looks worse than some AI art from 5 years ago
  
  That scene was good even if the CGI was bad. Or maybe I’m biased because I read the novelization first that included it.
- Neither James Camwron or George Lucas are theater people in the slightest. They're film people and both did works that were incredible technical achievements. Both of these guys are camera and lense and lighting and editing system nerds first and do the theater stuff so they can get a budget to do the technical stuff.
  
  Sorry, I'm adopting a "once a theater kid, always a theater kid" approach.
- I mean they have eyes. They look at the results and decide they like it. Looking at this, I think it looks worse, but it's not hugely different and I can easily believe it looking better in motion. (The picture in the body. The post-picture looks better in the version that has multiple colours, can't tell if that's new or old, but I doubt the technology chose to make it all blue on its own).
  
  I don't think the people at the top actually sit down and watch the entire process. They are just told it will make the picture "clearer" or "sharper" or "more up to date" or something, they're wined and dined and constantly told how "advanced" this stuff is. If they've put a lot of money into "updating" something they've done, they probably don't want to admit to themselves that they just wasted millions, they'll focus on the positives of it, rather than the negatives.

I can't even tell which side is before and which side is after
- In both pictures, the left is before and the right is after.
  
  Weird how it desaturates in the first one but adds saturation in the second one
- I, too, am a philistine who finds these changes to be, if not imperceptible then inconsequential.
  
  It might be much more noticable as an actual video, or at the full 4K resolution, but posting these low-resolution still side-by-sides just makes the OP look like a snob.
  
  I just thought the second one looked better on the right and the first one looked better on the left

Short answer

People act like True Lies is a good movie when it's insufferable. The Terminator is the only good film Cameron ever made. Maybe Aliens on a good day.
- excuse me way of water exists
  
  and the abyss

It's just a movie, not a full TV series or whatever. In absolutely certain the original reels or negatives exist to do a real upscale. For most things I'd rather just keep the original home release quality and leaven it as is, or at least DVD quality for most I should say. Horror movies should be vhs quality as well as certain comedies etc. But if you're gonna do it, don't half ass the process. A lot of people worked really fucking hard to make it look how it does and having an AI paint all over it and call it better is crap.

oh no the movie that literally inspired the "dirka dirka mohammed jihad" "gag" isn't preserved perfectly noooooooooooo retvrn pls
- Yeah, I’m not really a huge fan of this movie, it’s just the two examples that have gotten the most discussion. Cameron has applied this to several of his other films that have been re-released in 4k and it serves as a bad precedent towards how much filmmakers choose to manipulate and change their past works like Lucas did.

Oh, God. Cameron is going down the George Lucas route. Hearing Darth Vader scream, "Nooooo!" as he carried Palpatine and seeing people cry to that killed a part of me.
- DO NOT WANT!!!!!

which one's which?

The AI one looks so desaturated it looks like a Bourne movie

To be honest, the second picture dosen't look bad. It had a more modern photography that can hurt the sensibilities of people who remember it with a more hot color temperature, but it also dosen't looks like a TV movie now.

Link to the first picture: https://nitter.net/metaplexmovies/status/1735735555181223980#m
Link to the second picture: https://nitter.net/RazorwireRyan/status/1735752770295128195#m
- LOOK AT THE SHIRT!!
  There is literally, literally no possibility that his shirt isn't constantly warping frame to frame into random shapes. It's just reinventing the ripped parts, and his skin underneath. Insane!