Parents volunteering has a long history in the United States. Advocacy was needed when children didn't have a basic safety and health guarantee—a school building was in such bad shape that it would collapse on kids while they attended school.
Today, our school buildings are rarely in such dire conditions that parents need to voice their concerns. Instead, parents are more inclined to address invisible safety issues, such as emotional safety and specific physical safety (not from the physical building anymore but from hostility).
Many parents have experienced disagreements and misalignments in their schools. Often, the disconnections are so polarized that parents and children experience intense anxiety and stress in the school environment. In such a fearful state, parents believe calling the system for top-down discipline is the solution but are often disappointed by the response they receive.
Even though such expectations from families might be out of the school system's consideration for action, they have been sending a strong signal that the current school cultures aren't and haven't been working for students and their families. Failing to interpret and respond to this signal and letting problematic cultures run our schools is one of the main reasons people left the system.
System culture serves its purpose.
When I asked parents about their perception of schools' purpose (what is school for?), many had their own fantastic ideas. However, very few were aware of the actual objectives our schools are designed to achieve.
When we don't know, it's impossible to say, "We agree."