It's an outdated legacy of the farm economy. Adults still romanticize it. But those months out of school do the most damage to the kids who can least afford it.
That said, come on... are we seriously going to cancel summer vacation? Maybe we can make some serious efforts towards regular summer academic enrichment, educational experiences, and travel aimed to expose our children to new people, places, and things outside of their provincial worlds. Maybe schools can take the lead on such efforts, and quite possibly we could make it fun!