If a monkey uses a typewriter, there's no copyright.
If I use a typewriter with a monkey, I get copyright and the monkey doesn't.
Why would the monkey need copyright for me to get copyright?
Right, because monkeys cannot be granted copyright. If you use a typewriter along with Microsoft, the resulting copyright will be owned jointly.
This story isn't about a monkey claiming co-authorship, it's about Microsoft claiming co-authorship.