This gels with my experience (purdue physics/math grad 2011). It also reflected in the composition of staff for the departments. I think to field a robust math department you don't need the staff levels that you do to field a dual theoretical/experimental program in something like physics or chemistry.

e.g. at MIT the ratio of grad students in physics/math is 2.4 even though the undergraduate programs in Math (especially if you include Math+CompSci) are much greater

https://registrar.mit.edu/statistics-reports/enrollment-stat...