I agree and understand with what the OP is saying. I've often wondered that too. But then I think about it and maybe Mally wants us to see that she looks normal (well, more beautiful than most of the people I see, but still normal looking).
Here's what tiny, tiny bit I understand from watching useless TV. I saw a show that examined (through a series) what attracts people to each other, relate to each other, etc. There is a whole science to it.
For instance, I saw that if you want to attract (especially a male) wear the color red. Now you might say, "Gee! Annie, that's not new." But it isn't just the color red, the fact that it's bright, but so is orange (bright, that is). It all goes way back.
Anyway, my guess is that these models have been examined (facial structure, etc) and she its the mold (just like Stacy Ann is the model the Aussie uses for his shoes). Same idea, just different products.
Most of us don't realize but we are pushed, molded and cajoled into buying just about everything. From the way the products are placed in a grocery store to the models that are used on QVC.
So, that's just my take on it. Again, plus the fact that her skin originally is not in very good shape. Think about it. You don't really see her when they advertise Dr. Deneses' skin care products. I don't think. Maybe they do, but I don't think Stacy Ann is the only one sitting there putting on the product.
Don't start bashing me about not liking Stacy Ann. I don't know the girl. I'm sure she a lovely person. I am just talking about her skin. My guess also is that most of you ladies probably have skin prettier than her's or you wouldn't be so interested in skin care products.
I've seen her come on after she's gotten a terrible either skin peel or sunburn (I suspect the latter). A long time ago I heard someone say her mother was also a model. I don't know if it's something my brain totally made up but I thought someone said that. If so, that would reinforce my explanation for the science behind why some models are chosen for certain products and others for hair, etc.