I think you’re assuming money is there and families just aren’t doing the calculations to find it. I think parents are looking, but the money just isn’t there. How many bills, other than car insurance, are calculated by the number of people in the home? Cable isn’t. Internet isn’t either. Utility costs don’t change much with one kid gone either.
Food costs would change some, but even if we dropped the insurance on kiddo’s car and accounted for a dip in utility and food costs we’d still be short ~$15k/year for direct costs to our state school. Even after the direct student loan and ~$3k summer work earnings there’s a ~$7k/year gap, plus the costs of getting each kid to/from school 3x/year.
The ~$7k/year gap is only if those costs ALL disappear when one of our children is gone. They don’t. Our kids were all out of the house last summer. We weren’t suddenly able to bank an extra ~$600/month per kid. We don’t have an extra ~$28k for each kid to attend a residential college, and it’s not because we didn’t look for it. It’s just not there.