> Apple splitting their resources to support AppKit, SwiftUI, and Catalyst probably doesn't help.
Yup. After years trying to coalesce development around AppKit (transitioning away from the original Toolbox API), Apple decided to ship the org chart and simultaneously maintain three different UI frameworks, none of them fully consistent with the others. Engineering labor was divided between them, and extra work was created due to interoperability requirements. All three were left worse off as a result.