There were a ton of retcons in 4e Eberron that did not make it to 5e because the fanbase didn't like them (Baator, trying to organize the Orrery cosmology like the World Axis, anyone being allowed to gain Dragonmarks, etc). There are some retcons that did survive 4e Eberron, because the fanbase did like them (Dragonborn, Feyspires). There have been retcons in 5e that the fanbase embraced because of how cool they are (Daelkyr Dwarves, Warforged Collosi, Cyre 1313 and Dread Metrol). It's not that Eberron fans like retcons. It's that they like good retcons. Which I think I can say is true about most D&D players.
Like, take the new Goliaths. Goliaths up until the new PHB were always connected with specifically stone giants, not any of the other subtypes. But the new version introduces 5 new "subraces," one for each of the main 6 giant types. Which is, you know, a retcon. They changed the race's lore and mechanics without a metaplot justification and people accepted it. Because, guess what, most people think giants are pretty cool and having the option to be descended from/connected to any of the main giant types is just a good improvement to the original goliaths. If the average D&D player was as hostile to retcons as you are, they would never have passed the UA because there wasn't a metaplot justification for why Goliaths aren't just descended from Stone Giants now.
I am not saying that Eberron fans are a special group of people that are just more tolerant to retcons than all other D&D players. I'm saying that most D&D players are tolerant to retcons, it's the quality of retcons that determines whether or not people like it, not the fact that it's a retcon. I'm saying that you, for whatever reason, are averse to retcons in a way that most players aren't and you shouldn't assume the rest of the fanbase is as hostile to them as you are.