If nobody minds a new response to an old thread, I'll give you my reason why.
Security!
I have traveled to many, many countries by myself. I have also had many, many scares.
Cruising provides me with a safe place to sleep every night as well as knowing I can have a drink and not drive. Hotels are great but venturing out on my own in a strange country puts me on such an alert (watching my back) that I don't enjoy my experience.
I love the fact that I can book a tour with others on the same cruise who have no problem keeping me under their wing until we board the ship again.
Thanks to those who have done so in the past!