Personal space on public transport

There is not much personal space on trains. There is less on buses. I always think it’s funny how everyone sits half on top of one another but pretends no-one else is there. People don’t talk to one another or acknowledge other people. I’ve particularly noticed it when someone needs to move for another person to get out of their seat - etiquette demands that the person making them move says thanks, but the other person rarely makes eye contact or says anything. There are these funny unspoken boundaries that we are reluctant to cross.