To play devil’s advocate for a second: Figma, even as an Electron app on Mac, has far better performance than Sketch’s native Mac app. I find Sketch constantly gets laggy when dealing with large files while I rarely ever experience that performance problem in Figma. So while a native Figma app would be ideal, from a performance perspective they probably feel it’s not worth the dev time when they’re already getting such good performance from what they’ve got.

Making it look more like your other Mac apps doesn’t seem like a strong enough argument for the extra cost of developing and maintaining a native app. Figma’s detachment from the Mac-only ecosystem is precisely why it’s started dominating Sketch.