Note that minivans have been around longer than SUVs, but do not appear to be as disproportionate in fatalities. I suspect part of this is that they are typically lower to the ground and, more importantly, tend to only weigh about 500 lbs more than the average car at ~4500 lbs. Contrast this with full size SUVs, which are often taller and weigh on average closer to ~5900 lbs.