When I see both images, Beyonce picture seems to use front light so that her entire body lights up nicely without to much exposure but as well as not to dark but instead has soft shadows. The soft white light used to take the image also feels more natural. With the soft front lighting and her pose of her kneeing down on the grass and her hands on her stomach, it feels like elegance with beauty and care. While Demi Moore image is using Rambrandt lighting from the right of the camera with a more harsh light and stronger shadows. It feels more empowering, like as if showing that pregnant women are strong, independent, and with a huge amount of pride on her face expression.
Demi Moore announcement of her pregnancy was put on magazines for the time that it was taken in 1991. While Beyonce was put on her personal social media since now anything on social media can blow up so fast and spread around the world in less than a day compared to a magazine. Also making it easier to land on magazines everywhere.
My thought on the reasons for the different styles that the actress are doing is probably due to how during 2015 to 2018 people have been more open and publicly shaming women/mothers for breast feeding in public. Though the shaming started before the 21st century it started to become more public in recent years, so women tried to not get put within the cross fire of these debates especially actresses. while during the 20th century, women breast were being more sexualized and so women posing naked on camera wasn’t a huge problem, at least not publicly but they still had to censor or hide women’s breast on magazines
Annie Leibowitz used broad light for the Demi Moor photo. Ask yourself; “Is the subjects head in a 3/4 view?” if so it is either broad or short light.
I think the major difference between these two images is that Erizku relies on props to tell the story while Leibowitz relies of lighting and pose. As you wrote, in the Erizku photo the light is very even.