I'm not sure why it would be true that screen time is not a problem for a <1yr old. At about 6-9 months (maybe before) they are able to interact with the screen, and they interact much more with it if it has bright colors and responds to their touch. We would occasionally allow our eldest to use the phone around this age and she would become despondent if it was taken away. So we decided never to do that again.

Of course, a lack of interaction with humans could be a factor too but in our case we were literally playing with it alongside her and she would still get upset if it was taken away.