Forgive me, but isn't ABBA, the phenom '80s Swedish pop group, known for sunshine, lollipops, and roses? Isn't their synthesized music fodder for elevators and background music in pharmacies? Isn't the quartet famous for its international successes like “Dancing Queen,” “Take a Chance on Me,” and “Waterloo”? So why is Theatre Under the Stars' production of the long-running musical, Mamma Mia!, such a slog?

What a dispiriting show this is. Not much flash, not much substance, not much of anything. There are two outstanding performers – and voices – in Sally Wilfert, as mom Donna, and Felicia Finley, as bitchy backup Tanya, but everyone else in the cast wanted to get this show over with as soon as possible and go home. There's no life in it, no heart, no spinning disco ball. Even the glo-stick finale (those '80s icons given out during intermission) failed to galvanize the audience. It was sad. The entire evening was dull.

Somehow, don't ask me why it is so, but Mamma Mia! has been a perpetual smash ever since its London debut in 1999. It has played on every continent except Antarctica, being the sixth longest-running show on the West End and still playing, and the ninth longest-running show on Broadway, closing September, 2015. This jukebox musical has spawned innumerable revivals, two movies, and continues to draw audiences around the world. I don't get it.

I can tell you when and where I was when I first heard “Eleanor Rigby” by the Beatles. I vividly recall what I was doing when first I heard “God Only Knows” by the Beach Boys. I remember, in a haze, when I heard The Velvet Underground & Nico's “I'm Waiting for the Man,” and I definitely know when I heard Maria Callas in recital in Philadelphia. These songs are my musical madeleines. ABBA holds no Proustian memories for me. I know their songs – who doesn't if you grew up within a two-block radius of an AM radio? – but their bubblegum melodies and greeting card sentiments never infected my ear. I think I bypassed the group, or they bypassed me.

But this dreary show does the successful group no favors. Parochial and utterly predictable, Mamma Mia! traffics in shameless nostalgia for the pop foursome. Book writer Catherine Johnson came up with a somewhat original plot: Sophie's about to be married and she wants her father to walk her down the aisle. Trouble is, her mom Donna doesn't know who he is. During the free-love '60s she had three lovers: Sam, Bill, and Harry. (Why Sophie doesn't ask for a DNA swab from each prospective dad would put a damper on the proceedings, I guess.) She asks all three to attend the nuptials to find out who he might be, and the show shoehorns as many ABBA hits as possible into the drama, whether they should be there or not.

Director Dan Knechtges relishes the glitz and glamour of set designer Tim Mackabee's Greek island stucco walls and the lovely projections by Greg Emetaz – watch the windmills spin in the background, while the sheets on the clothesline waft in the breeze – yet these, other than Wilfert and Finley, are the only things alive on stage.

Jukebox musicals are the most difficult of genres. How do you arrange a pop group's greatest hits within a plot not manufactured specifically for them? Show tunes have a particular place and a very particular reason where they fit inside a show, ask Rodgers & Hammerstein or Stephen Sondheim. Jukebox numbers can go anywhere, so can the plot. Johnson gives ABBA a nice skeleton on which to hang the hits, but ABBA's numbers are so anemic and un-specific, they could be sung be anyone. That's why we don't get involved in this show, no matter how much fake drama is written around the pop tunes.

But if you're an ABBA fan, none of this matters in the least. You want to clap through “Take a Chance on Me;” see “Voulez-Vous” danced with a full contingent of high-spirited high-steppers (Jessica Hartman's choreography is full-on great); and watch Donna and her Dynamos strut through the Mylar curtain to regale us (again) with “Dancing Queen.”

It's all about nostalgia, baby.

Mamma Mia! continus through March 3 at 7:30 p.m. Tuesdays through Thursdays and Sunday, 8 p.m. Fridays and Saturdays; and 2 p.m. Sundays at The Hobby Center, 800 Bagby. For information, call 713-558-887 or visit tuts.com. $30-$134.50.