We scroll down and that becomes a "animation while scrolling". While its an unusual orientation, it believe it is the right one. Its not a time axis - its "time since the user was created".
The graph isn't a "this is how many followers the user had at this point in time" but rather "right now, here are all the followers this user."
A point is "the Xth user following had a join date of Y" and thus the X axis is in effect a time axis (though not a linear time axis).
From an eye scanning view, the horizontal bands are easier to follow and notice than vertical ones - and that is part of the goal of the graphic (to emphasize those bands).
The graph isn't a "this is how many followers the user had at this point in time" but rather "right now, here are all the followers this user."
A point is "the Xth user following had a join date of Y" and thus the X axis is in effect a time axis (though not a linear time axis).
From an eye scanning view, the horizontal bands are easier to follow and notice than vertical ones - and that is part of the goal of the graphic (to emphasize those bands).