I've seen Broadway shows for many reasons, and not necessarily the same one. Sometimes, it's advance buzz, or a star, or a composer or director or playwright. Sometimes, it's because I have a friend in the show or associated with it. Sometimes, it's just to get out of the rain and escape for a few hours.
Examples:
Cats OBC - Advance buzz from London plus the London cast recording
Hairspray OBC - Advance buzz, Marc Shaiman, and Harvey Fierstein
The Heiress - advance buzz on Cherry Jones
Fences - James Earl Jones, then I went back a second time for Mary Alice
Jersey Boys - wanted to see what the fuss was about
Grey Gardens - love for the documentary and advance buzz on Ebersole and Wilson
On Your Toes revival - I wanted to see George Balanchine's choreography on stage
Sweet Charity 1985 - I wanted to see Bob Fosse's legendary choreography on stage
Dreamgirls OBC - advance buzz
Mystery of Edwin Drood OBC - Betty Buckley, Cleo Laine, and George Rose
Les Miserables - had a friend in the OBC
Raggedy Ann - had a friend in the OBC (God, help me)
Smile - Marvin Hamlisch
Show Boat '90s revival - had a friend in the show
Titanic - had a friend in the show (that's the only reason)
Ragtime OBC - had a friend in the show, plus I loved the novel
Tango Argentino - free tickets
Precious Sons - free tickets
Phantom of the Opera - free tickets
Into the Light - free tickets
This is just a sampling ... so ... lots of reasons.
As to what makes a show successful? If we could come up with a foolproof answer, we'd be millionaires.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22