I always thought this perspective was funny because it always assumed what the people on their phones were doing. The assumption is that they are disengaged with each other when it's just as likely that they are talking with each other in a group chat alongside a few other non-present participants in the same group chat, and all trying to share photos with each other that they just took from the outting beforehand, or setting up a way to split costs in advance, or something else equally or more interactive than a conversation you can eavesdrop on.
Usually it's just shitty UX slowing them down.