"just" is doing a lot of heavy lifting here. people wasting time staring at screens is the prevalent problem of today. with TV it was not as bad because there was/is only one in a room so it becomes shared experience. phones are worse.
Go a little further. Think about "how." How do slot machines get people to waste their money for hours-on-end? How does TikTok use short-form video to get people to scroll for hours-on-end? What is the mechanism?
It's OK to waste time. All art and entertainment is a waste of time. Most of what people do on HN is waste time. Arguably anything besides eating and procreative sex is a waste of time.