There probably isn’t demonstrable factual answer for this, but the TM can do some pretty good speculating.
I live by a fairly busy thoroughfare that has one eastbound lane, one westbound lane and a center lane for left turns. it seems like every eighth car or so travels with their left wheels in the left turn lane. Why do people do this? They manage to stay in their lanes on two lane and four lane streets without left turn lanes. It’s not just this particular road, either. I see it often elsewhere as well.