Primarily because there's a line around the block to teach in a suburban school, and NYC had issues finding qualified black and Hispanic people to teach. DoE pays better than the alternatives, so until they find a rich husband, they're going to have to teach somewhere to pay back their student loans and then pay for a down payment on a home. With that said, the school in question doesn't have a good reputation, and it's zoned for mostly black, Latino, and South Asian working class neighbourhoods. So add in some rabblerousing activist students, social media, some Muslim kids, and black kids who are unlikely to have philo-Semetic views and you this level of lobo in a high school.
IIRC, these schools aren't as anarchic as say worst case scenarios you're thinking of from the DC and Baltimore metro areas. With that said, there way more spots available in not nice schools than in nice schools districts. If you're not Catholic, you can't teach in the few Catholic schools left. So it's either charter schools, or um, you earn $50K with that BA in teaching. For most teachers, they'll ride it out for as long as possible until they vest in the pension plan, their student loans are paid off, or a better school comes along. My friends that operate buses and subways in the worst neighbourhoods are in a similar boat.