Even without the Union factor, we knew the SSE was very difficult to even get that going without taking up a severe amount of development time.
Making a Story Mode now with a different kind of cutscene is going to still take up way too much time while other modes suffer. Ultimate at most had a more or two gone due to little time to do everything, and we only at worst really lost one mode(and no matter how you go about it, Target Test and its equivalents are harder to make work with a massive-sized cast. Even more notable is how long it takes to get whatever reward it is for them, which was already a herculean task starting in Brawl alone).
Voice-overs in every language to make it work? They already do that enough where it really counts(properly saying the character's name when selected). It's significantly more costly than is being implied here. Again, it's not simply a Union thing. It's a massive amount of Actors and Actresses being hired. It's even more noticeable when they recycle a crapload of stuff to make budget. They still have limitations budget-wise. Nintendo isn't making a movie here or a set of movies. They're making a video game. Priorities need to be on the actual gameplay first, and what is most popular, you know, having a large cast of characters people want. Recording that many lines for every character also takes a looooooooooot of time. Like, way more than it needs to be. Especially when said Story Mode is never going to be the most important part of the game. SSE only really was plausible due to using body movement as its core way to portray the Story, and it honestly did work just fine. Missing a cutscene or two did happen, and the closest thing we get to an oddity is that Ganondorf's portrayal is implied he might've wanted to become the true Big Bad by betraying Master Hand, but it's too vague. ...At the end of the day, he still joins the Smasher's sides and defends Master Hand from the true Big Bad, Tabuu, so the implications aren't delved into enough to really matter. He's still a nasty person within what he does, but simply may just be loyal(but it isn't the real Ganondorf, so that's hardly a big deal).