The more one is in the distance, on the Silk Road or a Trans-Africa, the current security situation, simple border crossings or a general exchange would be quite helpful.
Barbecue together, a cozy get-together around the campire, a hiss of a beer, badminton or a card game - there are a lot of things that are fun in a larger group. Or only becomes possible in a larger group.A campsite would of course also do this, but depending on the travel area there is no appealing place nearby - or the crowds of people overwhelm you after a few days of seclusion.
How can you meet other travelers? Here is a list of ways to get in touch with other travelers: