It’s not just students - it is the schools as well. Schools offering MPA’s or other degrees geared to government or public service encourage borrowing based on the IBR and loan forgiveness options. For example, see this presentation from NYU Wagner School of Public Service: https://wagner.nyu.edu/files/admissions/FPSLF_Program_Webinar_Slide_Deck.pdf
I don’t think it’s a bad thing for taxpayers to support graduate education that leads to public service – but I think that direct funding in the form of grants tied to the student’s commitment to work a certain number of years in specified types of jobs makes more sense.