It is a direct response to developer feedback - that they only are going to make iPhone apps because redoing design to support even just iPad, let alone a watch, TV, Mac, and AR variant is work. Even Facebook hasn't found the resources to port the Instagram app to have a proper UX on iPad.
This started with the separation of iPad OS (and release of Catalyst, and SwiftUI 1.0) in 2019. iPad OS is effectively the mother platform - an iPad app can be adapted down to target iPhone, or to target macOS and visionOS (with both those platforms also supporting running iPadOS apps natively without modification). The L&F changes in 2020 to macOS (with release 11) were heavily about making iPadOS and macOS more visually similar.
It doesn't surprise me at all that a team at apple tasked to make a consistent HIG and L&F across all products is borrowing heavily from the most recent HIG/L&F they worked on (Vision OS).
This started with the separation of iPad OS (and release of Catalyst, and SwiftUI 1.0) in 2019. iPad OS is effectively the mother platform - an iPad app can be adapted down to target iPhone, or to target macOS and visionOS (with both those platforms also supporting running iPadOS apps natively without modification). The L&F changes in 2020 to macOS (with release 11) were heavily about making iPadOS and macOS more visually similar.
It doesn't surprise me at all that a team at apple tasked to make a consistent HIG and L&F across all products is borrowing heavily from the most recent HIG/L&F they worked on (Vision OS).