LONELY at times. You are on alert for just in case as you have no one to assist you and are dependant on strangers.. From simple directions to more serious stuff like an accident.
A casual hike in the nearby forest no one knows you have not returned or where you might be found if for some reason a search is started. Maybe the hotel reports your "abandoned" luggage a few days later at check out time.
You do get to set your own schedule within obvious limits of business hours flight schedule and so on.
That you want spend an hour looking at some piece of art work a scenic view is your choice.
Some desire to travel alone. For example a married couple might separate and spend a vacation with their parents, their home town or whatever.
It can be a chance to meet others do your special hobby or interest that your partner is not interested in. For example one likes to scuba dive and the partner does not like the water. and prefers an adventure land based.
I encountered an elderly person their spouse had passed years ago. The children, grandchildren had scattered to many different towns and cities over the decades.
It was decided that the younger could visit the older . the elder just took an adventure once a month it might be a weekend to next city. A week at some resort.
A bus tour , a train tour , a cruise big planet lots of choices of places to go and method of travel.
The comment made I can sit at home and look out the window, I can do that too on a train bus, cruise, hotel room . THE SCENERY CHANGES.
Many never go very far from home or take the same vacation to the same hotel to the same room the same restaurant the same view year after year for decades.
Some just like to go to some other place for a peek at other places. A day in the forest, a day at a beach explore an historic site or whatever. not needing to always be concerned what the travel buddy wants to do.
Have seen many people argue over where to eat their lunch. One wants the exotic place the other the familiar one. One the sidewalk cafe the other the indoor place.
The one alone is free to pick the one they want.for whatever reason it is they want to give it a try. if the meal was good they might return again the next day.
I knew people that would check in their room place the appropriate map on the wall and just toss a dart and go there next. Some need to micro manage every second of their time.and do not like mystery or not knowing what they will find.
Travelling alone or with a buddy is just different.Some like to be attached at the hip 24 hours a day and do stuff together ALL THE TIME.
Some just go and do stuff by themselves. Of course being alone if you meet a person of interest you do not need to ditch your travel buddy.
It is prudent to check in with back home, the hotel desk , the ranger station or whatever on a regular basis