That's part of it. Also the bit about Amadeus Arkham being some sort of nutcase, and there's a degree of supernatural stuff about Gotham being haunted or something as well. There are lots of different explanations that all go together.
>Being that anything can be changed as soon as a writer changes
Theoretically that's the case with any work of fiction. It doesn't even require the writer to actually change. It could just be the one writer changing his mind. That doesn't matter since it is still canon, and has been referenced heavily for at least 30 years as far as I know. Even if some new retcon came along and said all those older explanations were actually incorrect all along, there are still tons of stories that treat them as true, and those stories are the ones that continue to influence the public consciousness, so much so that they've been used in a hit video game series, some of the most successful movies ever made, multiple cartoons, and a live action tv show. And even if it was retconned in the comics, which would be highly unlikely with a popular element like this, it would also likely be changed back either once another writer got the chance (which is very frequently since there are so many Batman comics every month) or simply once the writer "reveals" that the idea just a ruse by some villain or something all along. Popular elements tend to stick around, or even be incorporated if they're from another continuity originally. That's why the comics adapted Harley Quinn, and the Mr. Freeze origin, and have continually tried to adapt Batman Beyond, even though it never quite works. By the same token, that's why popular elements that have been removed over the years, like say Bat-Mite, have been re-introduced, with "reveals" and "remembering" that they were canon all along.
Honestly Batman is a bad example for this since his corner of the DCU isn't really affected by major retcons or universe altering events very much. Batman: Year One is his Post-Crisis origin, but it doesn't really change much from his original origin from 45 years earlier, it just expands on it. Batman was practically unaffected by Flashpoint, which caused major problems actually, with things like Robin Rises making it a plot point that the Justice League is scared of Darkseid because he hasn't been seen except for the one time the Justice League fought him in their origin, but also the same story flashes back to Batman fighting Darkseid in Final Crisis. Of course later they "reveal" that history being fucked is an actual plot point caused by Doctor Manhattan, so that "fixes" that too. The point is that they don't like to change Batman because they don't like to change popular elements, and Batman is always very popular.
>& history is constantly altered creating new universes that change up how things work constantly.
Not quite. The current DCU is the same universe that's almost always been used since January 1945. Technically earlier stories were retconned to be a different universe (Earth-Two), but the broad strokes of stories for characters that existed in both Earth-One and Earth-Two remained canon anyway. And then later Earth-One and Earth-Two merged so both were canon in the main universe anyway.
Earth-One became New Earth which became Earth-0 which became Prime-Earth. They just changed the name to New Earth when other universes got merged into it, and then to Earth-0 when other universes were copied from it (because they'd need a new name to differentiate it from the others. Don't know why they didn't go with Earth-1 though. Earth-1 would later be revealed to be a different, unimportant failed comics line of an Earth). Also they changed the name to Prime-Earth when two other timelines got merged into it with Flashpoint, but Prime-Earth is a fucking stupid name, and technically it's still also officially called Earth-0 by The Monitors, but it is useful to have a different name for the different eras. They didn't change the name after Zero Hour changed history, and that's a bit of a pain, honestly.
You played all the way to the fourth one, then that one made you retroactively hate the other games? But you obviously liked them since you played up to the fourth one.