I am not picking you here. I think your view is increasingly common. In my opinion there do seem to be cognitive consequences to longterm 'smart' device usage. I would not be surprised if people in 50 years we look back on smartphones as we now look back on cigarettes. After all there was a time when most of everybody also just viewed cigarettes as a mostly harmless recreation and pleasure in times when you'd otherwise be doing nothing. That they were severely damaging your body over decades of use is probably something that did not really surprise that many people, but it was also something that was far from entirely certain. Similarly to today, I doubt many people would be especially surprised if there were indeed cognitive or other consequences from longterm 'smart' device usage, but it's still something that's far from entirely certain.
Being deep in thought doesn't transport you into higher plane of existence. You still need somewhere to fix your eyes so you don't look like a lunatic on a packed commuter train where people are apparently judging your aptitude based upon where you're gazing.
When you get into the habit of filling every bored moment with whatever you can find in the phone, you start to lose the ability to stare off into space - maybe out of the window, maybe close your eyes - and let your brain put together bigger thoughts.
It doesn’t help that there are a lot of things on your phone designed explicitly to try and addict you to them, either. It can be hard to put down the phone even when you know damn well you’ve gone through everything interesting in whatever apps you’re addicted to.
Try looking at another person on public transit for more than a few moments and see how uncomfortable they get. It's not a question of anxiety it's just etiquette.
In most public transports the noise would make any conversation impossible anyway even if it would be considered acceptable and normal.
Observing people can be quite fascinating and illuminating.
In Europe the outdoor seating at cafes face the street so you can easily people watch without straining your neck.