Wild guess: Boston is a densely populated city with geographic restrictions (due to the bodies of water around it). The ratio of roads needing to be cleared vs

Wild guess: Boston is a densely populated city with geographic restrictions (due to the bodies of water around it). The ratio of roads needing to be cleared vs available snow dump areas might be a lot higher than in most places in Canada. Also this was a very extreme snow year for them, so it wouldn't make sense to set aside this much land for snow dumps every year.