They're valued at $4T, they have hundreds of billions hoarded. They could run 50 billion dollar startup projects and not feel it. Imagine a startup getting handed a billion dollars ... and the vast knowledge that Apple has access to already.
There's no way they couldn't do a better Siri. For some reason, they just ... won't.
here is a clue delivered -- money does not make software better, and lots of money often results in worse.. it makes no sense? actual experience begs to differ.
Classical homework assignment -- the Mythical Man Month and related essays
Heavily funded startups have terrible track records in reality. The only cases where it seems to have worked is when the money was used to undermine the market dynamics by nuking competition via severe underpricing.