If she's a single mom living in a bad neighborhood, she likely can't afford after school care, if she makes more than would give her a subsidy, but not enough to have extra money. Even the YMCA or Boys and Girls club will run you a couple hundred a month (at minimum). I know I struggled with paying for after school care and I make a fairly decent income - it's just really tough when you only have one income that is typically not great.
Most after school care closes at 5 or 5:30 - usually not past 6. For a working mom with a communte it's hard to get there by that time. So riding the bus home from school may be the only way he can get home from school.
I would suggest that she "trade out" with another parent. They do "after-school", she takes the kid overnight on Saturday. This way it's free for both of them.
I used to live in Chicago (in a "bad" neighborhood, where I paid $1200 per month rent, by the way.... yet drive by shooting and police raids happened on a more-than-weekly basis). My daughter NEVER played outside. However, when I picked her up from after-school, I had packed a dinner and we would drive to park outside of our neighborhood and "picnic" and then she could play. She can also try that.