You’re only considering highways.
I see roadside memorials all over the place on non-highways for people who were going to fast.
Where do you live. Here in the NY metro I only see them on highways. There is one on Laurel Hill Blvd in Queens near the gate of Calvary cemetery but that spot is dangerous because, for some reason, drivers fail to see the red light as cars are exiting Calvary. 3 or 4 people have died there that I know of in the past few years.