All of this is contextual and it doesn't take a screen or a book for someone to give off clear vibes of not wanting to chat. "Mind if I sit here" in a crowded shop is the expectation. Anything beyond that such as having a conversation with a total stranger depends on the subtle behavioral cues given off by the other party.

It's not my intention to be rude but based on your responses on this topic I'm guessing you're fairly oblivious to the relevant social cues. There's nothing wrong with that per se but adopting an attitude of "not my problem" is probably just going to aggravate the people around you.