If the PGA says I’m supposed to do more work with modalities to maintain my certification, I don’t have modalities at my school to use aren’t I still just “checking the box”?

Because the goals you develop in the PGA should take into consideration your weaknesses and strengths, as well as your environment and other factors (such as whether you plan to stay in that environment) addressing modalities may not be part of your professional development or you may want it to be because you plan to change jobs. The PGA is dynamic and not solely focused on weaknesses.