Let's get the biology out of the way first:
Since humans eat plants & other animals, there are no novel (physical) nutrients that an Ogre can't get elsewhere. They're just conveniently packaged.
And then let's deal with some cultural history:
Simply because you all but equated Ogres with Polynesians (Maori, in specific), we should perhaps take a look at Maori cannibalism. It was a thing, and a very nasty thing to boot.
As soon as Europeans first met Polynesians in the Aotearoa, Capt. Cook noted that the locals had a preference for fresh human flesh. In Jan 1770, he noted: "though stronger evidence of this horrid practice prevailing among the inhabitants of this coast will scarcely be required, we have still stronger to give." While we should always be careful not to cast undue aspersions, the practice has been known in Aotearoa long after Cook's time, and was also known in other related cultures.
Paul Moon, a New Zealandish historian, treated cannibalism in This Horrid Practice. The Maori had access to an amazingly broad spectrum of food from root crops to birds to plant produce to seafood. Lack of food wasn't the cause of cannibalism. It seems to have been a product of their war culture. Moon notes "post-battle rage" as one factor. Retribution for offences, especially given by an enemy, and as a warning to other tribes are other important factors.
Other scholars note that cannibalism is deeply rooted in the culture, in the onomastics and in the lore of the Maori.
Ogres are not a different and separated species of humans or hominids, they are more like a wide spread tribe or ethnic group of people
Since Ogres are humans based on the Maori, there is no real nutritional reason for Ogres to heat other humans, we must consider the historical, mythological, cultural, religious, and folkloric reasons.
Ogres are ... heavily affected by an inability to produce or obtain normal nutrition from ordinary food forcing them on divergent dietary choices.
This clue is something of a red herring. People can get food from just about anywhere on the planet. Since Ogres are humans too, it stands to reason that they'd be similarly gifted.
If they are unable to procure food in ány area they live in, they're unlikely to get it from humans. Historically, humans are pretty good at savagely exterminating anything that gets in their way. Once Ogres develop a taste for other humans, other humans will develop a taste for eradicating Ogres.
Who knows? They might even develop a taste for Ogres!
Ogres are also affected by gigantism and have a mutated form of MC4R which makes them incredibly effective at saving energy and conserving fat more so than Māori people (mentioned the Māori people because they are genetically good at getting tall, big and athletic, no racism intended)
Since there's nothing particularly special about Ogres in regards their ordinary humanity, I think the answer will be neither biological nor nutritional. Like the Maori, your Ogres have simply practiced cannibalism for so long that it has become thoroughly embedded within every aspect of their culture.
Their mythic & legendary heroes did it; ordinary warriors did it; everyone else benefited from it. For them, it's no different than meatloaf on Wednesdays. So entrenched is it that places are named after the practice, a rite of passage must be when a young suitor offers some crispy fried human tenders to his beloved, there may well be special utensils for eating various parts of human, like the 'oqnoq, which is a very long handled sharp pointed spoon used to punch through the sinuses in order scoop out the warm brainy goodness from the skull.
As time progresses, there may even be specialty shops in Ogre towns dealing with the various rubs & marinades that go with human cookery. Perhaps even decorative tins shaped like human faces & breasts & thighs, for those hectic holidays when you just can't be bothered going out and butchering a fresh human and all that's available last minute is tinned minced human and you want to at least decorate it up real nice for the family get-together!