and also why things can change during an episode production, sometimes it can be due to the animation studio messing up (in the simpson case, what was meant to be the original pilot of the show had to be redone because the animation wasn't that good [ it was "some enchanted evening", here's an extract of the original https://youtu.be/sx-wjF5AMmk ]). The early season production also had their share of drama between those working on the show and already by season 4/5, the group making the show would change.

This kind of stuff is why I wouldn't say i'ts automatically a problem that something wasn't originally planned, as long as it fit within the story, I won't have issues with it (and beside, what was original planned could've been worst too or changed for good reason, per example I think shortening the fight between scrooge and bradford in the ducktales finale work better since it give more impact to scrooge defeat for me+the episode had a limited run time so it'd make sence to cut some stuff that aren't a 100% necessary to it). Tho I do think people need to have verifiable source to claim X part of a story wasn't planned, I don't like when people make it up or take interview out of context to argue part of something wasn't planend to attack it, it happened with the webby twist per example and it feels like most of the discourse on its production is based on rumint. And if an actor was mistreated, I'd also ask for pretty good sources on that too, not just rumint (if frank angones really mistreated tony anselmo, I think we'd have more soruces than just reddit or tumblr thread talking about it, donald isn't a obscure character and tony woudl've been pretty vocal if he was too)

On the simpson production, I'm currently reading this french book on the show, it goes from their debut as shorts to the 2020' https://www.thirdeditions.com/products/bienvenue-chez-les-simpson-lincroyable-histoire-vraie-de-la-serie-culte it does sources its claims and give insight to the show production, I did watched "some enchanted evening" on W9 while they were doing pretty long primes in french but I didn't knew it was originally meant to be the pilot.