Public education caters to the common denominator…the public. If you want higher rigor and standards set for your children, then you will need to find alternatives - which, in some areas, are no better than the public schools.
I wouldn’t blame the system for poor standards. Their standards are actually decent for most children. The problem is that teachers are forced to spend a significant portion of time and energy on classroom management.
Couple that with the fact that most parents aren’t reading to their children at night, so those kids grow up falling behind the curve. Reading comprehension drops -> other subjects follow suit. Rinse and repeat each year, and you eventually end up with high-school seniors reading far below their grade level.
The teachers now have to scaffold all of their content. The kids who didn’t fall behind? They receive no attention from the teacher who is instead focused on helping the kid with a 3rd grade reading ability to try to understand the content.
An indirect tragedy of the commons, where parents are relying on public education to raise and teach children with no input of their own.