Do most people who travel with the group don't know each other?

That's not necessarily true. Even if you don't know each other, you can find your own friends. If you are alone, it is best to be with someone who is also alone, so that everyone can have a companion and take care of each other. If people are with friends and family, it is more difficult to blend in. Once I was traveling with a group alone, and I met a friend who was also traveling with a group alone. We had a good talk. Later, we became pen pals and met two people to travel together 10 days. It feels very good.