A remaster is generally a re-release of an already existing game. It is a new build of the same game, on the same engine, with the same assets. The only difference being compatibility with new hardware, etc. In my opinion, a lazy cash grab that realistically shouldn't even exist. Often times these new builds aren't even the same and have many bugs not originally present in the original game that the remaster developers never even fix.

A remake should always try to stay as close as possible to the original for its initial presentation. The intention of a remake is to become the current market replacement of an old product, for various reasons. Maybe it doesn't run on new hardware or the original code was deleted/lost. Maybe the original game was poorly received and the developers want to try again with some QoL adjustments. Maybe the graphics haven't aged well but the story is timeless. This is why a studio would opt for a remake instead of a lazy remaster.

The issue comes from something like Silent Hill 2 Remake. It did not include a "Classic Mode." The remake alters some pretty important themes in the game, changes multiple story elements, and entirely changes the focus of the gameplay, putting a greater emphasis on action and combat than the original ever did. The remake shifted the tone away from a melancholic exploration of a character into a Hollywood action movie with an over-reliance on jump scares (basically every Bloober game, honestly).

This has problems when fans attempt to talk about the game. Which version is each talking about? People do not always specify. If one person talks about the Coin Puzzles in the apartments for example, the clues, hints, and solutions are completely different between versions. Players of the original game needed to get a crate of rotten juice cans and drop it down a trash chute in order to receieve a coin for that puzzle, but that entire sequence was removed in the remake. This is only a minor example that doesnt impact the story, but the problem of discussion disconnect is apparent. You can imagine how confusing it would get when there are other major changes that do impact the story later on in the game.

These differences are fine if the developers add them as an "Arrange Mode" or "Remake Mode," but not as the only way to experience the game. That effectively says "our new version is the only good version, because we won't allow the players to directly compare the two with the same engine and graphics. If you want the old version, you can't, because we definitely aren't selling the original and pirating the original that we refuse to sell you is copyright infringement."