They shouldn’t be plotted that way technically. The big 5 are independent traits so they should essentially be sliders, not linked like that.
That said, it’s way easier to see the points when you do that. Easy to miss when colors swap, for example, without the lines when you’ve been looking at this stuff for a few hours.
Maybe (as in I would have to check, not that I think it likely) at highway speeds. But in any low speed area, vehicles without gas engines can be sneaky.
My company was working on an electric bus and I saw a driver sneak up on an engineer with the aforementioned city bus. They actually, legally (in some places) need noise makers at low speeds to deal with this.