I'm not a shareholder but buying equity in OpenAI seems to be a much better deal (for Disney) than making OpenAI just pay royalties, no? Seems like everyone wins, unless you think OpenAI will never amount to anything and it's all a bubble.
Cash from royalties doesn't disappear like equity value would, in the event of a bubble pop.
Bird in the hand is worth two in the bush and all that.
If you destroy your brand value in the process? This is an entertainment company... The entire value of this company is the characters and the right to make new stories with them.