OP, you gotta understand that not all parents care about small class sizes as much as you do. Small class sizes mean ability groups are harder to make. It's harder for everyone to find a friend. The kids get tired of each other socially. And it's harder for the school to admit siblings of current students, which matters a lot to those families. It also necessitates hiring more staff, and it isn't that easy to find good teachers. Maybe using undesirable space as classrooms, like partitioned hallways or trailers. And a bigger total enrollment of the school makes it a lot easier to support good sports and activities.
You're also thinking bigger class sizes pays for some nice-to-have extra. But really, bigger class sizes covers the basics that people take for granted. Smaller class sizes across the board would mean painful cuts that people really don't like.