Most people who join a travel group are single or their spouses do not enjoy traveling for whatever reason. Or it could be that most of their friends are married and their single friends may not be able to afford to travel. This was the situation for me.
When you travel to different locations, you may not be going with the same people each time. The group I belong to is quite large and usually there are about a dozen trips available to choose from each year.
But people are friendly when traveling and once you share a room (if that is what you choose to do), eat meals together and go on various sightseeing expeditions together, you get to know them and often build friendships in the process. You will find very few that you don't want to spend your time with.
From the last trip I took, there are seven of us that get together occasionally and one in particular I keep in touch with by monthly luncheons. However, we may or may not go on the same trips together again. Most of the people I met this time have done more traveling than I have so may not want to go where I would like to go. But that is fine because there are many other great people in the group. And traveling together is definitely a way to get to know your traveling group better.
When you travel as a group, you fly together, stay at the same hotels, many of your meals are provided so you eat together and when you explore, you travel together by coach bus with an explanation of the landmarks you are visiting. Some share rooms to save on costs while others prefer to get their own rooms. And there is always ample free time where you can do something on your own if you need some alone time or go with one or two others if you are like me and are afraid of getting lost. I have been lost in a foreign city before and I didn't like it.
There's no doubt that traveling with a spouse, a family member or a very close friend is the most ideal way to travel but group travel can include comaderie, hilarity, fun and the chance to make new and perhaps lasting friendships. If a spouse or a close friend doesn't enjoy all of the things you do, when traveling in a group. there's probably someone who will.
So if you are in a position where you want to travel but have no one to travel with, joining a group might be just what you're looking for.