The loneliness and vulnerability of being on your own for long periods of time is certainly not for everyone. You can feel free to stay in a city for weeks if that is what you desire. You set your schedule. For example, finding accommodations is easier as you can take the last available bed in a hostel. A table for one is easier to find than a table for four.
People are usually more hesitant to approach larger groups of people.
Not so if you are on your own. You'll be surprised how many people approach you when you are traveling by yourself. You will blend in and become enveloped in the local culture rather than standing back and looking in. There is nothing worse than feeling ill or being injured while traveling solo. If you do travel on your own, your trip may cost you a bit more than if you went with someone else.