It might be that they don't agree with how the money is currently spent. I see a lot of waste in my area. There are also some odd or overly restrictive policies. One can agree with the goal of funding of education while disagreeing on whether the current money is promoting that goal or being wasted.
Well, that's the entire universe of public spending.
In a properly socialized society, there's a shared understanding that some goods are going to be paid for collectively. We might not all agree that they're all "goods", for example vegan parents might object to paying for some other kid's meatburger; but perhaps they should set up their own vegan school, if they can find enough good vegan teachers.
So there's waste in public expenditure. A lot of that waste occurs in private expenditure too; bear in mid that most UK schools contract-out the provision of meals. If those schools are wasting food, that's private waste. Some of the waste will be corruption; so some proportion of the cost of a public expenditure programme has to be audit and monitoring.
In general, in the UK, public money is handled pretty carefully. I suspect that in the USA, it's handled even more carefully; there seems to be a long-standing view that public expentiture is identical with waste, and should be stopped.
Not sure what specific waste you're referring to.
My state pays well. However, increasing pay is not going to get many more or much better teachers. The teachers I know would rather work for less money at a private school because there's less bureaucracy and better policies. I have a friend who completed his student teaching and decided not teach because the school policies sucked and the kids were terrible. He took a lower paying non-teaching job instead.
We can't make parents care about educating their kids. But some districts have teachers barely getting by, or struggle to hire due to low pay. It doesn't sound like the area where your friend works doesn't have this problem, but generally teachers should be able to live on their salaries.
There's an obsession (around here at least) that the schools need more money for fancier stuff, and that somehow this will produce better grades.