they get lazy about using/doing non device things.
That's the key. Over the generations media (from books to smartphones) got more sophisticated in grabbing our attention to the point that addiction really has become a problem. While everything fun can be somewhat addictive we now have corporations optimizing their products in that way.
I'm sure kids can develop healthy habits with phone and internet consumption but I also believe they need help by restricting exposure in order to play "conventionally". It's similar to sweets - if you leave kids to just eat whatever whenever they want, they'll stuff themselves with candy until they vomit repeatedly.