The animation and VFX artists in California are unionized. For example, here's the Animation Guild [1] and the list of studios covered [2]. It's basically all the big names plus many of the small ones.
What the union couldn't do is prevent jobs from offshoring: the jobs moved to Vancouver, Montreal, and wherever else the tax credits were. I think it's still the case that the studios are getting like a 50% tax rebate on Canadians working in film in Vancouver. When your staff are "half price", that's hard to compete with.
I think you're conflating animation and VFX. They both have different stories than the Japanese anime industry this article is about. These [1] are the kinds of studios I think of for VFX and none of them are in the Animation Guild.
The Animation Guild has been around since the 50s. There were fights in the 70s and 80s over offshoring. In my experience, in the past few decades the Animation Guild has great training programs, medical and retirement, but doesn't really swing its weight around over employment.
VFX was completely separate and has never been unionized. There were efforts in the 90s that turned into the Visual Effects Society, which is more about promoting VFX and recognizing achievements. There were efforts again when Rhythm and Hues closed the same year it won an Academy Award for Best Visual Effects that also didn't go anywhere.
I'll be honest in saying that I didn't consider the American experience. The article and video in question was about the Japanese Anime industry, which as far as I could see, works by contract direct to animation studios, without union representation.
What the union couldn't do is prevent jobs from offshoring: the jobs moved to Vancouver, Montreal, and wherever else the tax credits were. I think it's still the case that the studios are getting like a 50% tax rebate on Canadians working in film in Vancouver. When your staff are "half price", that's hard to compete with.
tl;dr: it's not a lack of unions.
[1] https://animationguild.org/
[2] https://animationguild.org/about-the-guild/studio-list/