Why do "bad" schools exist?

I was watching this video about how NYC schools are funded. Basically is per child, and then extra money for whatever extra services they need like special needs or esl.

But by this logic, why do some schools appear to be worse than others if funding isn't the issue?

also I found out they're spending 30k a year per child. But maybe that number factors in things not directly related to the kid I'm assuming? Seems quite high lol. Or maybe it's normal and I'm just dumb. 3.3k a month (30k/9 months).

*Public schools. I am referring to public schools.