There is a shortage of grad students in many departments.

Cutting PhD students would require cutting the number of undergrad students educated and classes offered to them. This would prevent science and engineering students from getting their bachelor's on time because of requirements for science sequences. An undergrad 4-year degree becomes 5 years long or aren't completed at all.

The need to expand class offerings to teach undergrads requires TAs to teach labs. Our department is already over-offering classes compared to the number of grad student TAs.