Three factors: Color, personality, and realism.

First, color and shading.

vs.

The predominant style of the day in anime employs very crisp cell shading and eye-watering colors. Both female and male hair and eye coloration comes in any range of colors, from neon to pastel to white (although female characters most often display this). The typical color for skin in anime has gradually lightened to almost pure white over the years. Additionally, modern anime has a very specific, hard method of shading and highlighting that makes hair and skin look unnaturally shiny and often gross, lowering the realism value and throwing the texture of the skin into uncanny valley territory.

Secondly, anatomical proportions. Besides the shading, female character body and facial proportions have degraded so much that they are barely caricatures of human anatomy. Here are some examples of female anatomy in early anime:

and some in modern anime:

The biggest changes have been to the breast to waist proportion. For some reason, anime producers believe that an E-cup is the appropriate cup-size for an average 14 year old Japanese female. Bodies have also lost all of their depth (that come from an illusion of thickness necessary to two dimensional media) in favor of being skinny and flat (except for voluminous breasts, of course) and many normal, attractive parts of ladies (ribcages, stomach pooches, and natural folds) are simply smoothed over. Another noticeable change has been to the eyes and facial shape. Anime noses and mouths are apparently inversely proportional to eye shape, size, and distance apart. As the size of the eye increases, shape becomes more prominent, and distance towards the ears increases, the size of the nose, mouth, and chin decrease, contributing highly to the uncanny valley effect many modern any girls have.

Take these faces:

vs these

Thirdly, anime girls have lost much of their visible personality over the years due to moefication. This has happened to male characters also, although to a lesser extent. Anime girls are often not allowed to make cartoonish expressions (deemed unattractive) or generally change their expressions at all barring blush lines. In producers’ efforts to make the girls attractive to the audience in every frame, they sacrifice any personality that they might have. Anime girls look increasingly similar to one another, differentiated only by their hair style and eyes. Granted, there has always been a problem with female character same-face syndrome since the conception of anime (actually, in all drawn media) but as the number of female main characters in anime has grown, ironically, the problem has only increased.

Wow! Anime girls with the same hair color that you can actually tell apart!

And somehow, girls with all different colors that you can’t.

The screenshots in this post were taken from Urusei Yatsura, Neon Genesis Evangelion, Nadia: The Secret of Blue Water, Ranma ½, Kimagure Orange Road, Ping Pong Club, One Piece, Angel Beats, Higurashi When They Cry, Sword Art Online, Shakugan No Shana, and Chobits. The examples above were not used to bash any anime, but merely to demonstrate the evolution of anime art tropes from the 1980s to now. The writing and plot of each anime were not taken into account at all.