Who has gone alone and why?
Two part question here. Who has gone alone?
I have. Several times.
My first visits to WDW were with family, sometimes with my children who are older and have children of their own, several visits with my spouse which were also very enjoyable, and one with my oldest son, his daughter, her husband, and their two daughters. (three generations on that trip. lol.)
While these have all been great trips, it occured to me that a solo visit might be fun as well. And after that first solo visit, I have made several drives down there alone, and have yet another planned for November of this year as well.
Second question was
WHY?
That's easy too. Here are a few of the reasons a solo visit to WDW are so much fun.
No waiting for others to:
(1) decide what to do next
(2) take photos
(3) rush right by the street performer you would really like to watch
(4) take multiple rest room breaks
(5) mill around and study the map
(6) stop to trade pins
(7) not be interested in visiting the restaurant you would really like to try
(8) stop for every character that pops up
(9) stop to press coins in some silly machine
(10) walk super fast when you are really worn out
(11) stop at every gift shop in the park
(12) insist on taking a break at the resort in the middle of the day
(13) not being ready to go early in the morning
(14) stop to rest when you are ready to move on, &/or not wanting to stop when you need to rest
(15) not wanting to repeat an attraction that you would like to do again
I could go on listing, but you get the idea.
A solo trip is a great trip, at least for me it is. (But I'm still ready to go when family members are ready to go as well.)

Karnak