The government economy of teachers, police, jails, medical services grows though. And they vote Democrat. That's what this is really about. Without that growth the Democrat employment and retirement systems collapse.
Imagine a failing business with the power to re-write a nation's laws not only to insure their survival but their growth in size, power, and wealth. That is big, bad government. Once a runaway train of government reaches sufficient speed it can't be stopped until the big crash.
That "growth" is more like the "growth" of a balloon when you put more air into it. Those illegals are a net drain on state finances. Without more workers producing, the state tax revenues decrease. So, even though schools get more funds allocated for having more students in the classroom, the source of those funds is shrinking.
Californians tried to avert this situation when they voted for Prop 187. Sadly, the Democrat overlords could not allow this proposition to take effect--they value power above all else, and do not care about the long-term effects on society or the economy as long as they can consolidate and grow their absolute power. So we are now starting to see the outcomes of all of these progressive policies, and it is not pretty.