Why are Headshots Being so Tightly Cropped by Photographers?

I have attached a screen shot from google image search on modern headshots  - as an example...
Which images draw you in to look at the person , or even to linger on a persons image among a sea of other peoples images? We are inundated daily with tons of social media selfies/avatars and headshots as we surf the web. 
The individuals who really created the idea that a fabulous headshot is a necessity, were actors, and entertainers.
People who needed to get noticed ... people who know that the casting directors might look through 3000 images in a day ,
looking for just the "right" look for a role.  They all know that they NEED to do something to stand out in a crowd. 
So, recently photographers have started to follow their trends in the headshot business...
In the sampling below, we see how a lot of  headshots are being done by the most elite of photographers nowadays ...
and the reason for cropping in so tightly , isn't because we want to zoom, in or be artistic.
The reason is because studies show that the images we tend to gravitate towards, are the images that succeed in capturing the personality....
and the personality is where? in the eyes.
So  compositionally speaking, our eyes tend to be drawn to cross points of a compositional rule of thirds...
and that means in a headshot, the eyes should be  in the upper third of an image. ... this often means cropping off a piece of the head, hair or even the forehead. 
Now I know , we all went through our childhood knowing someone whose mother or friend could never seem to take a photo without cropping someones head off...
and this would later become ingrained in us that this is how we can measure a good photographers abilities.
I challenge you to post a couple of images of yourself, and see which ones get the most traction.
Notice that most of the time , people will be drawn to one of two things, either an extremely interesting facial expression ,
or else a close up - that shows something of your personality in your eyes... Close enough for someone to see it in your thumbnail or avatar...
(which, lets face it - the thumbnail is where most of our headshots end up being used the most...)
So let your personality shine in a compositionally attractive way... AND close enough that people CAN be compelled by it, even from a distance.
 
(click to enlarge)