They actually deliberately changed the nomination rules for the Animation category a few years ago because too many lower profile art films were getting nominated. Sure, they weren't winning because the entire Academy votes in the actual categories but the previous system did mean that several spots were reserved for non-Disney/non-Dreamworks films. Since then it's basically one "art film" slot, maybe two, with everything else being big studio films.
For instance, the first year under the new system had the following nominated films:
The Boss Baby
The Big Bad Fox and Other Tales, Mary and the Witch's Flower, The Night is Short, Walk on Girl, and a few other films were also released that year.
A Silent Voice also came out that same year. I'm still bitter how THAT didn't get nominated, but fucking Ferdinand and The Boss Baby did.
It's gone to Disney or Pixar 15 times out of 21…. and while they definitely deserve a lot of those, particularly the Ratatouille/WallE/Up/Toy Story 3 streak of superb films... they don't deserve to be winning basically by default.
I saw a report that Disney/Pixar have now won the Best Animated Feature in 9 of the last 10 years since 2012, with the exception being Into The Spider-Verse, and quite frankly? They really didn't deserve to win the majority of them.
For me, ParaNorman, The Wind Rises, Kubo and the Two Strings, Klaus, Wolfwalkers and Mitchells vs. The Machines were more deserving of winning in those respective years. Also Big Hero 6 only won because that was the year where The Lego Movie got infamously snubbed out of a nomination.
It really feels like they should rename the category to the "Disney/Pixar Award" because, with the aforementioned Spider-Verse exception, it really feels like if your movie isn't made by Disney or Pixar, you don't have a snowball's chance in hell of winning.
And I guarantee we'll be going through this same song and dance next year when Lightyear inevitably wins over Across The Spider-Verse (Part 1).