On the other hand, newer cars have gotten more dangerous for pedestrians. Safety is indeed a luxury.
Some cursory research turns up some interesting characteristics of the increase from 2010 to 2020.
• It was almost entirely in urban areas.
• Over 2/3 was on non-freeway arterials. Only about 1.4% was at intersections. (The percent of pedestrian deaths at intersections is around 16%)
• 90% was in darkness.
• It was adults. The rates for children continued to go down. For the years given above they were 2.7, 1.6, 0.8, 0.4, and 0.3 per 100k.
Cars did get heavier from 2010 to 2020 by about 4%. That would mean 4% more momentum at a given speed and 8% more kinetic energy but when dealing with getting hit by things that weigh a lot more than you do velocity is more important than momentum or kinetic energy [1], so I doubt that this was a significant factor.
Cars with shapes that are less safe did get more common, so that could be a part of it, but from where and when most of the increases were it seems there is a good chance that it is not so much that cars themselves but the behavior of drivers (and to a lesser extent) pedestrians that is mostly responsible.
Distracted driving due to phones, speeding, and reckless driving are all way up.
[1] Would you rather be hit by a Fiat 500x at 60 km/hr or the largest freight train ever constructed at 0.2 km/hr (since we usually don't talk about speeds that low to help visualize it at that speed it takes 18 seconds to go 1 meter)? The train would have 500 times the Fiat's momentum and 1.7 times the kinetic energy, but I'll definitely choose to be hit by the train. I'd even pick the train at 1 km/hr, where it has 2500 times the momentum and 42 times the kinetic energy. (Going the other way, a typical 9 mm bullet has 1/1500000th the momentum of that 0.2 km/hr train, and 1/87th the kinetic energy, but I'll the the train over the bullet).