Maybe my impression isn't accurate - but aren't there countries where it's the norm (or at least, not uncommon) for strangers to ask to sit when there are plenty of seats? Just for the conversation?
When I was still in HS, some mornings I'd stop at the bakery - which had a little cafe - on my way to school. Every morning there was a group (a "liar's club" in some parlances) of old gents. Some businessmen, some retired, definitely a connection between them. They would discuss current events, bringing in the historical angles, making value judgements... tsk' tsking.... all of that. They would let me sit with them sometimes. I didn't talk, just listened. Guess they saw some value in that.
On the other hand, if I'm having a private convo and don't want to be disturbed - my nanosecond instinct is to flash the trespasser with "the look". I don't care if they're harmless or not; I'm guarding my space. LOL.
