

Social media sites thrive on the engagement that comes from those people doom scrolling so this whole premise is antithetical to the purpose of social media sites and the only reason they aren’t doing the same to children is because the law prevents them from doing so wholesale (but they will try to edge around the law every chance they get).
People are lonely. They lack the kinds of interactions in their lives that make them feel comfortable and more importantly allow them to feel seen or understood. The mindless scrolling temporarily fills the void they have in human interaction while allowing them to interact themselves if/when they want to.
Humans are “addicted” to human interaction and the algorithms take advantage of that fact to make a product out of them.
Additionally, human brains seek out novelty. A lot of our day to day lives are filled with work and duties (chores, bills, children) etc. People in the 1920’s weren’t addicted to the news paper. They needed something to do with their free time that didn’t break the bank. Increasingly there’s just not that many things that you can put down to switch gears that fit that bill.