The large factors are phone use (more prevalent among american drivers and there's data to show this), and homelessness - the homeless are dramatically overrepresented in US pedestrian deaths and the population has increased dramatically in the US over the past decade. Even more so though it appears to be attitudes, Americans are twice as likely as Europeans or Canadians to say using a phone while driving is acceptable. Though no single factor is a smoking gun, vehicle size is one of the least convincing. Getting hit by a 4000lb car or an 8000lb truck matters much less than how fast the vehicle's going (let's all remember our high school physics class).
This blog post is the best deep dive I've seen on the data: https://www.construction-physics.com/p/more-on-us-pedestrian...