“What is happening, Sweetlife!?”

That bit of banter Saturday from Fitz and the Tantrums singer Michael Fitzpatrick probably wasn’t meant to spark an existential crisis in the crowd at the annual music-meets-food festival at Merriweather Post Pavilion. But it raises the right question:

What is happening, Sweetlife?

The event that in its first four years became one of the East Coast’s most forward-thinking music festivals — presenting a still-upstart Kendrick Lamar, offering a first glimpse of Los Angeles sisters-with-guitars Haim, delivering a revitalized Strokes — was, on its fifth go-round over the weekend, stricken with an unmistakable blandness.

Some of the blame falls on a lineup that felt one-note, built as it was upon a collection of less-boldface names whose primary purpose was to deliver agreeable party music. Bastille, catapulted to the big stage by its single “Pompeii,” was fine — and an apt substitute for Coldplay — while Foster the People singer Mark Foster sounded nasal.

How many acts could offer a rumbling bass and hand claps? And how many appeared contractually bound to egg on audience participation?

For those who bothered to watch, nearly all of them.

Good thing, then, that many of the nearly 20,000 people in attendance — high-schoolers mostly, some checking in mere hours after coming home from the previous night’s prom — didn’t bother. They flirted and partied and roamed in packs, tried to score beer from the relatively scarce grown-ups and pulled out wadded-up dollars at the stalls of the festival’s secondary “lineup” of local chefs and their trendy food.

The only force who could move these teens was Lana Del Rey, the waxen doll of a singer-songwriter who worked her downbeat voodoo over the largest crowd that a Sweetlife act would see all day.

Everything that has been said about her performances is true but one: The performer — whose career was very nearly tanked by an awkward, but not awful, 2012 “Saturday Night Live” appearance — can actually sing, particularly when she is delivering her most affecting banshee wail.

On Saturday, Del Rey played up that voice in a remarkably aloof way, moping about the stage while her band — which included a guitarist, bassist and pianist on a very un-Sweetlife grand piano — did most of the heavy lifting.

It was confounding how little the singer had to do to win so much adoration. There seemed to be so little effort till she delivered her ace in the hole: After a winsome performance of “Blue Jeans,” the singer, clad casually in jean shorts and cowboy boots, simply hopped into the crowd to take selfies with fans, kiss and hug them (languidly) for a full two minutes before climbing back up and launching into her new song, “West Coast.”

“She’s so beautiful,” one teenager cried after the show, boiling down Del Rey’s unusual charm. “She’s so unique.”

The flood who had come to see her missed out on the last minutes of the set by rapper 2 Chainz, whose talent proved why hip-hop is a boon to such festivals as Sweetlife. He sliced through the day-long malaise with his hits, including a rendition of Juicy J’s “Bandz a Make Her Dance.” Only the number of teenagers bouncing around to the song about strippers was eyebrow-raising.

The infiltration of the very young, and in very scanty attire, had some folks over the drinking age worrying about the ubiquity of belly buttons and cheek-
revealing jean shorts amid the (admittedly less worrisome) flower crowns.

Being worried about “the kids” of America may be a generations-old story, but what is new is how all these crop tops and bra tops are codified by social media. Instagram and blogs practically dictate what young people wear to music festivals — whether they’re roasting in the California sun at Coachella, or swaying to electro-pop in a far-flung suburb of Washington. It’s Stevie Nicks without any sense of history.

More evidence that there is a sameness from festival to pop festival: Sweetlife was an exercise in branding, a marketing opportunity for all, it seemed, but the bands. You could fill your Sweetgreen-branded totes with free gluten-free chips, ancient-grain energy bars and pricey water bottles. Charge your phone at Uber — only, of course, if you were willing to download the car service’s app. You could spin State Farm’s wheel for free sunglasses, or check out a video camera no bigger than a thumb.

Did the music fare better than the branding? The soul-pop act Fitz and the Tantrums and Los Angeles native Nicky Blitz had been here before, snagging spots from acts who might have been more compelling. That they were now Sweetlife veterans did not seem to have earned them any loyalty. They played to half-engaged crowds — the former playing a sped-up, sexless version of the Eurythmics’ “Sweet Dreams (Are Made of This)” that pretty much explained the disinterest.

By mid-afternoon Saturday, a light rain began to blanket the outdoor venue. The acts Capital Cities and St. Lucia — both relegated to the B stage amid the trees in Columbia — did a lot to revive the event’s flagging energy, if not provide some sonic sunshine.

St. Lucia took the stage just before 4 p.m. in a uniform of bright Hawaiian prints that matched the band’s breezy pop and transported the crowd to a beachier place.

Capital Cities played a set of crisp, modern disco punctuated by the sounds of live brass just as the skies cleared. “It’s good [expletive],” the band sung, from its track “Farrah Fawcett Hair.”

Eh, mostly it was just okay.