When I first heard about Tilda Swinton’s “The Maybe,” an ongoing performance piece in which the actress sporadically sleeps in a glass box at the Museum of Modern Art, I sighed and shrugged and laughed a little. Another unoriginal work becomes a cultural flashpoint — cause for media outcry, cause for real, live spectacle, an unexciting performance sold to ticket-buying tourists as avant-garde. What can you do? But “The Maybe” wormed its way into my head, and I found myself confoundedly returning to it often. It was only a week or two later, and after reading Jason Farago’s takedown in The New Republic, that I realized why I cared: middlebrow.