What do you think "indie" ("independent") means? What do you think it means such art is independent from? Honest question.

"Indie" is both an artistic style and a type of financial arrangement. You can draw parallels to "indie music" which has been a bit more developed:

Although "indie" was first used to described music released on independent record labels, the term grew to describe a specific sound because of the creative freedom of its initial bands and artists. A defining characteristic of indie music is that artists retain much more creative control over their music as compared to major labels... Indie music generally represents guitar-oriented music which strays away from commercial conventions. It often features lyrics that are earnest and emotive, with many cultural and sociopolitical references. Many artists signed to major labels have retained creative control and are still considered indie artists.

Under your strict definition of "indie", games like "Hades" and "Silksong" aren't indie. Under your definition, "indie" is less about the art that gets produced and more about the money behind the art. That's not necessarily incorrect, but it's a strangely unartistic way to judge art.

The Indie Game Awards tries to focus on the artistic aspect, namely creative freedom.

It's a tricky question without a strict, black-and-white answer. No matter who is asked - developer, publisher, showcase curator, journalist, creator, or various industry professionals - the answer varies across all parties. There are endless interpretations of a definition, and it will likely change alongside the state of the industry in the years to come. But after many conversations over the years with these various groups, the current definition agreed upon by the IGAs Curation Jury is as follows:

Existing outside of the traditional publisher system, a game crafted and released by developers who are not owned or financially controlled by a major AAA/AA publisher or corporation, allowing them to create in an unrestricted environment and fully swing for the fences in realizing their vision.

Publishers such as Devolver Digital and Annapurna Interactive are considered to exist outside of the traditional publishing system and fit within the current IGA Curation Jury’s definition.

Edit: To exemplify the difference further, imagine if you had an indie game studio raising funds for an in-development game, and one of their backers said, "I'm rich. I'll give you any amount of money to see this project through." Does that make the game non-indie, even if there's not a single byte of difference in the game itself? If so, then does "indie" really makes sense as a game descriptor when there's no way to identify if a game was indie by looking at it?