Compare how it is to sit in a bus next to a person who is engaged in his cell phone and one that just sits there straight up and down. You will discover that the seats are not wide enough for the passengers if one of them keeps on with his mobile.
It becomes too crowded, because the one who looks down at his mobile must keep their upper arms in a position that reduces the space and makes it uncomfortable for the passenger on the side.
Make a try and think about what you think you should do about the inconvenience.