Because it is proven that phone usage is not an addiction like drugs or alcohol. People put phones away easily if they have a reason to do so.
Thousands of deaths every year are caused by drivers on cell phones. You'd think they'd have a reason to put them away.
The main idea here is that overuse not equals addiction.
[...] the majority of research in the field declares that smartphones are addictive
Though that section continues on to disagree with that majority, "the majority" declaring smartphones are addictive is certainly supportive of them being so.