What's with the huge difference in file sizes on the Illustrator and Photoshop version downloads (~200MB+) vs Sketch (~3MB)?

PSD file size I could understand if they had rasterized the 2 color icons but shouldn't vector AI file sizes be similar to the vector Sketch file sizes?

Illustrator's .ai files have a fairly huge base size. An empty document is over 640 kB.

I think there's a bunch of stuff in the file to support older Illustrator versions -- PostScript libraries, stuff like that...

.sketch file doesn't include bitmaps.