In a traditional profile, a student owns or rents an instrument. When it starts to crack or rattle several adults interact. Tuition free music schools that provide rent-free instruments are tasked with procurement and upkeep. The teaching artists (TA) that they hire are usually gigging professionals who are paid by the hour to give group lessons to the kids. Each TA has to tune up to 20 sets of strings before class can start.
They don't have the time or the training to address warped bridges or frozen fine tuners. I have visited a half dozen small, independent inner city music schools, and I can tell you that routine sound and appearance issues are just endured not repaired. Given the choice, would you rather re-hair the bows or make the payroll? The city has several hundred more violinists because the people behind low income music opportunities are willing to take on the challenges, and operate on a shoestring budget.
I learned begging from Damian Lugue, age 9 (below). If you have anything I can use, please think of me and these kids.