The answer, as Morris freely admits, is that the maverick director-choreographer actively disliked Dryden's story, a complicated affair about Arthur's quest to unify Britain and rescue his beloved from his evil enemy, and has thrown all of it out, keeping only the opera's lovely Baroque score. He then uses that evocative music -- none of which was ever sung by the character of Arthur -- to create a song-and-dance pageant, using seven onstage singers (plus an offstage chorus) and 16 members of his talented Mark Morris Dance Group.
As he has so often done in his work, Morris manages to both eschew and abandon tradition, often at the same time. His dances, beautifully performed, are very much in the style of the period -- including an absolutely gorgeous finale with his cast dancing around the maypole. (The fairly minimal set design is by Broadway veteran Adrianne Lobel.)
But Morris is also never one to shy away from adding an anachronism -- as in the Beckettian sequence with a man briefly trapped inside a refrigerator. As is Morris' wont, the two-hour piece is also filled with more than the occasional extraneous touch, like a small parade of dancers dressed up like animals -- a moment that allows famed costume designer Isaac Mizrahi to engage in some genuine whimsy -- or a sex-tinged sequence that incorporates some sublte gender-bending.
If Morris' ensemble of dancers are often the focus on the opera's staging, his singers not only hold their own, they happily play along with his sense of fun. For example, the silvery-voiced soprano Sarah Jane McMahon does a little juggling (clad in a gorgeous Mizrahi take on the little black dress), while the excellent baritone Daniel Mobbs not only crouches within that refrigerator, but in another section, sings clad only in a pair of white boxer shorts.
Finally, Arthur is not completely ignored by Morris -- a gold crown is ever-present on the stage, presumably to represent his royal presence. A king deserves nothing less.