(warning: studied Math in college, so don't know how that biases me in this discussion)

I wonder if some of this is because of the number of jobs in industry for each discipline? There are a great many jobs available which nurture CS skills but I can't quite think of a job besides academia off the top of my head where that lecture in Toric Varieties I took would come in handy.

Maybe its that there is a career/financial incentive to go deeper into CS but not mathematics?