Men not graduating as much as women, must be mens fault for not studying enough. Women not earning the same as men, must be mens fault. Boys being isolated and depressed, must their video gameing and porn habits. Girls getting mental illness from social media, must be social expectations we stack on girls and women. Men getting worse outcomes in hospitals? Must be their behavior. Women getting worse outcomes in hospitals? Must be bias by doctors against women. Why are there more men in prisons? Must be testosterone. Why more women at home taking care of children? Must be cultural.
Any observable difference between men and women, can be describe as either being caused by external factors like social expectations or internal factors like behavior and hormones. Whenever I see researchers doing a comprehensive and deep study to explain why something is observed more in one gender than the other the usual answer is a tiny bit of biology and a huge (dominating) dose of culture. Such answer generally does not change base on gender, so if we are asking why social media is causing mental illness more in girls and boys, the answer is likely a tiny bit of biology and a huge dose of culture.