I think there are 3 reasons why IMG isn't promoting Jessica as much as other models:
1.
IMG intends to have bigger promotion on those who recently often appear in major campaigns and big magazines' editorial. If you notice carefully on the front page of imgmodels.com, many models such as Karlie Kloss, Karmen Pedaru, Joan Smalls... appear 2-4 times in different ads and covers, by which means they have had higher exposure to the rest of fashion community and the world . To casting directors, this group of girls is more 'trendy' to use hence the feedback for whatever productions these girls are involved would be stronger. I know this sounds horrible but it is just like a boutique would place their most salable products in the display window. Jessica has once been placed on the top shelf for a long time years ago, but currently she is less ambitious in getting major ads and covers, resulting in a exposure and investment chances reduction.
Maybe you will be skeptical that: Oh, but Jessica always attends events and give public speeches, that is exposure as well! Yes, but these might not be assigned by IMG, these exposures have nothing to do with her agency. In a way, Jessica has become
independent from her agent, leading to the fact that it would move on to give attention to other models who have larger needs to get jobs though the agents.
2.
Upcoming models and girls with special attitude/characters has become another investment targets of IMG. Although Charlotte Free is not a big name, her pink hair almost shapes her rebellious character and people would be left strong impression of hers. Therefore IMG has to put her on the front page. Another example is Xiao Wen Ju who is Chinese (proof of nations diversity) and has interesting facial features, plus she got the Kenzo campaigns, I-D, Elle and Glass Magazine cover as bonus points, so she is on the front page. Third example is Sky Ferreira, who is not only known for her work as a model, but her music as well.
Compared to the mentioned girls, Jessica is less thrilling to see. Part of the reason is that her special doll face isn't on trend anymore, and she does not stand for any kinds of special personalities. If I ask, if Charlotte Free, let's say, looks rebellious and Freja looks androgynous, then how does Jessica look and what does she stand for? For me, this is a difficult question to answer, it would take me a while to think about it.
When IMG considers which model should be put on the 1st page, Charlotte Free or Jessica Stam? Based on the above reasons, it must be Charlotte Free.
3.
Undoubtedly, IMG has to put a few greatest names such as Kate Moss, Gisele, Eva Herzigova, Daria Werbowy on the front page. Jessica of course is one of the big names but she does not compare to them. I feel pissed when I see Kate Upton, Candice and Miranda Kerr being put there, not because I dislike them but they are not well-rounded models. They are just Victoria Secret Angels and merely popular. They are more like celebrities than real models. However, it is just the way it is...they always cause a buzz! If I ask a random friend of mine, he is more likely to know Miranda Kerr than Jessica Stam. This is the reality, the more a model is talked about, the more she is recognized.
In my point of view, unless Jessica got at least 4-5 magazine covers or 2 major ad campaigns in a year, she would not be put on the front page on imgmodels.com. Although those numbers are just my assumption, but look at the models who are put there, 90% of them got such amount of work to present yearly, apparently this is what it takes for those girls to be put on the top shelf.
*All the above are just my personal thoughts*
And, I remember Jessica has been on the front page on IMG website once. The picutre is in black and white and she is biting her thumb in it. It has been posted on her thread in fashion spot, but I don't bother searching for it from more than 1500 pages. If I ever see that again by chance, I will post it. I wish all the Stam fans here can help looking for that photo/post too