Some people just don't want pictures of their kids all on the internet. It could be seen as borderline paranoia by some people but I think everyone has the right to the level of privacy that they want.
The best form of taking secure photos of your family is to take photos with a dedicated camera with it's own memory card. Develop the photo into a hard copy and keep the image digitally stored in your own systems and never share it online.
Also CSAM detection algorithms are known to misfire on occasion (it's hard to impossible to tell apart a picture of a naked child sent for porn purposes and one not send for that) and people want to avoid any false allegations of that if at all possible.
Yeah, babies are cute and all, but they all look the same for the first few weeks. If Everyone just had a standard library of like 20 or so pictures of newborn babies and everyone just picked one and shaired it instead of pictures of their kid no one would notice.