Depending on how much Kremlinology you want to indulge in, this is either…
(a) Apple recognizing what tools its users use, and providing useful assets
(b) Apple is giving in by not promoting the platform-native Sketch app and accepting they are being washed away by the tide of cross-platform Electron apps†
(c) Apple is engaging in a Big Corporation conspiracy with Adobe, the probable new owners of Figma, to lock you into proprietary subscription software forever and ever
† yes, I know Figma is not Electron, it is a wild cross-platform browser runtime unto itself, but you know what I mean
They have provided really quite good Sketch UI kits up until now.
https://developer.apple.com/design/resources/
Depending on how much Kremlinology you want to indulge in, this is either…
(a) Apple recognizing what tools its users use, and providing useful assets
(b) Apple is giving in by not promoting the platform-native Sketch app and accepting they are being washed away by the tide of cross-platform Electron apps†
(c) Apple is engaging in a Big Corporation conspiracy with Adobe, the probable new owners of Figma, to lock you into proprietary subscription software forever and ever
† yes, I know Figma is not Electron, it is a wild cross-platform browser runtime unto itself, but you know what I mean