When you consider that distributed repositories are going to be cloned dozens, hundreds, or thousands of times, it starts to add up.
Even if this larger project could handle that bandwidth, it is a significant factor for smaller projects, or larger projects like github. Meaning more of a chance that git remains the dominant choice.
The repo is hosted by third parties, bandwidth is not an factor (it's all text in any event so the compression factor is huge). There are actual differences worth talking about, file size is not one of them.
git repositories aren't giant masses of text files; they're compressed on disk and the additional gains from compressing them with lzma are minimal (12 MB on a 306 MB git repo I have lying around). I assume Mercurial does something similar as the difference would be a lot larger than 17 vs 50 MB if not.
Even if this larger project could handle that bandwidth, it is a significant factor for smaller projects, or larger projects like github. Meaning more of a chance that git remains the dominant choice.