I have always connected this problem with automatic cars. I haven't looked at statistical evidence, but I think this is a much bigger problem in the US than the UK and I think it's because it's much easier to drive an auto with one hand.

I often see established vloggers and public figures recording themselves with a smartphone while driving and they always seem to be American.

I believe there has been some adjacent research done into the safety of manual cars which has found that they can be safer since they demand more concentration to drive.