I can only speculate but my thought would be implementation complexity. Bitmaps work fine for say 99% of interface elements and graphic elements and they are a lot simpler to implement. Vector graphics just aren't a high priority I suppose.I mean, they aren't even natively supported in most operating systems anyway.
As per resource usage, vector graphics actually use less disk space. Rendering requires more CPU than bitmaps, but I doubt it's something Apple couldn't handle with a warning in the documentation.
As per resource usage, vector graphics actually use less disk space. Rendering requires more CPU than bitmaps, but I doubt it's something Apple couldn't handle with a warning in the documentation.