Well, it's easy to make that argument if you inflate the numbers ridiculously. You're not losing 30% of your kids or anywhere near that, and while public school enrollment is down, charter schools are a drop in the bucket:

Some non-made-up numbers:

Contrary to some theories, there’s no evidence that families are fleeing public schools in droves or for charters and private schools. While the city’s enrollment dropped by about 100,000 students since 2019 — not counting 3K — overall enrollment in city charter schools has grown by just over 10,000 students, or by 7.8%, since the pandemic started. And over that same time period, the city’s private schools actually saw a 3.6% drop in pre-K-12 enrollment, according to state data.

>Why the fuck is this so god damn hard for non teachers to get. Do you people just work in places where splitting things up doesnt INCREASE cost?

Because people care more about their kids' educations than the contentedness or wellbeing of teachers in a system that doesn't focus on their kids' educations. Sucks, but this is what happens when the public school system is so corrupt, bloated, and unable or unwilling to handle misconduct.