From my experience, I think a lot of parents are frustrated by it because these new methods for teach math (which are objectively better than rote memorization, I think) are so foreign to them that it's hard for them to help even their first graders with math homework. I've never been a math whiz, but I honestly found myself stuck sometimes just simply not knowing what the teachers expected from my kids. They've taught the kids all these methods to solve the problems that work, but require you to google what it is when it simply says "use X system to solve the problem." I'm open-minded about new methods, I'm fine with having to figure stuff out myself, and I actually appreciate what they were trying to do, but damn some nights were a struggle; especially when I know the answer, know perfectly valid ways to find the answer, and I know my kid does too, but since we have to use this specific math tool that my kid can't describe or fully remember and I'm completely unfamiliar with it.
It's not hard for me to see many parents coming up against something like that and then just blaming Obama or whatever, and leaving it at that.