Sketch is an interesting one, gained so much traction for having a superior interface but after several years in the lead it's getting devoured by a cross platform web app with superior collaboration.
It's relevant that has also been essentially 10 years of stagnation on the frameworks that Sketch is built on, i.e., AppKit, as Apple focuses on UIKit. In this case specifically Apple hasn't added best-in-class collaboration features to AppKit (or UIKit). I'm not sure whether it would have made a difference in Sketch vs. Figma, but the fact that they haven't has made it difficult for Sketch to compete, as Sketch's MO is leveraging Apple's built-in technologies.
