It's clear they don't have the in-house expertise to do it themselves. They aren't an AI player. So it's not a mistake, just a necessity.
Maybe someday they'll build their own, the way they eventually replaced Google Maps with Apple Maps. But I think they recognize that that will be years away.
Apple has surprisingly good quality AI papers, a lot of work on bridging research and product.
I agree that they don't appear poised to do it themselves. But why not work with Meta or OpenAI (maybe a bit more questionable with MS) or some other player, rather than Google?