From the article:

The import/export feature, which Apple demonstrated at this week’s Worldwide Developers Conference, will be available in the next major releases of iOS, macOS, iPadOS, and visionOS. It aims to solve one of the biggest shortcomings of passkeys as they have existed to date. Passkeys created on one operating system or credential manager are largely bound to those environments. A passkey created on a Mac, for instance, can sync easily enough with other Apple devices connected to the same iCloud account. Transferring them to a Windows device or even a dedicated credential manager installed on the same Apple device has been impossible.

You can create a new passkey in each password manager, though! As a one-off, it's not so hard, but it will become more work when you have lots of passkeys.

The FIDO Alliance, the consortium of more than 100 platform providers, app makers, and websites developing the authentication standard, has been keenly aware of the drawback and has been working on programming interfaces that will make the passkey syncing more flexible. A recent teardown of the Google password manager by Android Authority shows that developers are actively implementing import/export tools, although the company has yet to provide any timeline for their general availability.

...

The transfer feature, which will also work with passwords and verification codes, provides an industry-standard means for apps and OSes to more securely sync these credentials.

There are a lot of people who assume that vendors are always trying to lock people in. Sometimes that's true, but not always.