In the travel world there's a bit of a separation between those that travel independently and those that travel on a tour. I'm a tour girl. It's not that I don't like to travel independently, but I tours suites me better.
I'm often traveling alone, I occasionally find a friend to travel with; but I travel so much and sometimes quite far away that I can't always find someone to travel with. I don't really like to travel alone either, it's lonely. I know I could meet people along the way, but what if I don't? The thought of traveling to foreign cities for 2 weeks without meeting people, or constantly meeting new people but not connecting with any of them is daunting. Imagine having no one to really talk to for 2 weeks, to discuss the things you did and the things you want to do. If you're on a tour then you have instant friends (ok, I know that sounds bad.) But you're with people who are more or less in the same boat and with the same interests. And if you keep your tour in the 2-3 week range you're unlikely to get to know people's annoying habits. But there is a certain comradery that develops on a tour. Picking place to see in a city, helping each other with problems that arise, sharing knowledge, and getting to know another culture through meeting people from different places. There is a lot to get out of a tour socially, and I'm still friends with many of the people that I travel with.
Then there is the idea of planning the trip - hotels, transportation, dining, ugh! I don't mind it, but it is a lot of work and sometimes more then I have the time and patience for, especially if you're looking at seeing a lot of places in a short period of time. A tour makes all this easier.
But there are some cons to traveling with a tour: you do often end up being sheparded around in a large group (though there is a lot of free time too,) being stuck with annoying people, limited control over your schedule and time. Overall though, I've enjoyed all the tours I've been on, felt they were a good value, and the people were absolutely worth meeting and getting to know. I am however looking at expanding the types of tours I use. A bus of 50 people is great, but I think a smaller group of people is better.