I agree that kerning is also a problem, and I also agree that it it can't practically be fixed.

However, even if it's theoretically possible to change the font size, would Github ever do so? My impression is that as an organization they place a high value on interface stability. Very little about how I interact with the site has ever changed.

I suppose that individual publishers might stick in a hack to increase the font size, but a bad default means that as a consumer, I'll be stuck looking at tiny math on Github for the vast majority of documents.