The shape of the vehicle has far, far more to do with pedestrians dying than the weight of the vehicle. I would MUCH rather go over the hood of a 4800lbs Tesla model S going 30mph than under the front bumper of a 3900lbs Tacoma.
IIRC average car weight has been stable for ~20 years, not increasing, and also pedestrian deaths have been decreasing over the same period, even as people are buying big weirdo trucks and whatnot. Also, I'd expect increased prevalence of active safety features is more important than the weight of the vehicle for pedestrian safety.
That said, the rate hasn't gone up if you look at a 30-year timeframe, but it's a worrying trend nonetheless. It's a bit confusing though because I think you'd want to look at this per-capita. The absolute numbers show a 10-year upward trend, and the per-capita numbers are only split out by age group and show that same 10-year upward trend except it hasn't gone up at all for people under 20, which seems surprising.
But I remain confused because the 10-year weight increase is very small, less than 10% or so, so it is not clear to me that increasing vehicle weight is the most important factor. IIHS mentions road design and front-end design, but not weight as key factors.
