Some people (cough, cough) follow their favorite shows much like those individuals who follow players of their preferred sports teams. Others see their fave shows repeatedly over the years (cough). It gives them great joy, much like fans of their favorite pro hockey drama on cable. Broadway shows appreciate their fandom because they fill seats. Theatre is definitely a business....sometimes a cut throat business....(i.e. the recent firings / non renewals at Chicago).
"Noel [Coward] and I were in Paris once. Adjoining rooms, of course. One night, I felt mischievous, so I knocked on Noel's door, and he asked, 'Who is it?' I lowered my voice and said 'Hotel detective. Have you got a gentleman in your room?' He answered, 'Just a minute, I'll ask him.'" (Beatrice Lillie)