I don't know the history, but I think Figma predates much public knowledge about Skia.

Further, I have the impression that Figma has pretty specific and complex graphics needs. For one example of the sort of thing I mean, we decode image data in JS and put it into GL textures without the Wasm side ever seeing the pixel data, so that the browser can (potentially) decode on a background thread and uncompressed pixel data doesn't contribute to Wasm heap memory usage. However, I don't know Skia well, so it's possible Skia has some mechanism to composite GL textures it's not responsible for too.