One thing I think about is how Alexa is apparently considered a failure at Amazon (https://arstechnica.com/gadgets/2022/11/amazon-alexa-is-a-co...). Alexa devices sell well but people only use them for trivial use cases that are hard to monetize.
I speculate that Apple doesn't see a need to invest in Siri because the market has shown that digital assistants don't synergize with "services" that well.
Additionally, I don't think that Apple will need to leverage the "Siri codebase" as a starting point for releasing a compelling LLM codebase - maybe voice recognition, but who knows.
Apple has shown through other product launches that they will take a "wait and see" approach and release something when its ready.
I also think they're a protective measure to keep people from getting someone else's smart device, which might lead you into someone else's ecosystem.
The bullet points I see on the above page, in order, are - really good speaker - Siri integration - integrates with Apple ecosystem for playing music - smart home integration - "private and secure" whatever that means
So, it's not clear to me that "a better Siri" would necessarily result in selling X amount more speakers to make Siri a worthy investment while investing in better audio technology does because it's the main selling point for HomePods.
I very much think it has to be in their near future.