Why is Gimp JPG so large?

[Ofnuts]

The file size is modified by two factors:

1. The "chroma-subsampling" (by far the best bang for the buck) in the advanced options. Quartered chroma yields half the size of full chroma, independently of the "quality" setting.
   
2. Compression loss level (a.k.a. "quality"). The sweet spot is around 80-85.