Why didn't Merope Gaunt turn into an Obscurus?

Question

In Fantastic Beasts and Where to Find Them, we discovered that any witch or wizard with their magical powers repressed eventually turns into an "Obscurial". In the Half Blood Prince, we learned about how badly Merope Gaunt was treated by her brother and her father. She knew only rudimentary magic and ran away with a muggle when she got the chance.

Answer 1

Merope never suppressed her magical abilities

Obscuruses develop under highly specific circumstances, which don't appear to be satisfied by Merope's situation:

Newt: Before wizards went underground, when we were still being hunted by Muggles, young wizards and witches sometimes tried to suppress their magic to avoid persecution. Instead of learning to harness or to control their powers, they developed what was called an Obscurus.

^{Fantastic Beasts and Where to Find Them (2016)}

An Obscurus is the repressed energy of a child who is forced to hide his or her magical talent. This energy can manifest itself as an entity on its own that can erupt in violent, devastating fury.

^{Fantastic Beasts and Where to Find Them: Magical Movie Handbook "Beasts" The Obscurus}

An Obscurus is developed under very specific conditions: trauma associated with the use of magic, internalized hatred of one’s own magic and a conscious attempt to suppress it.

^{JK Rowling's website FAQ}

While Merope unquestionably suffered terrible abuse, and that abuse was related to her magical ability, she was never directed to supress it, or taught to hate it, the way Creedence Barebones was; quite the opposite, in fact (emphasis mine):

"Pick it up!" Gaunt bellowed at her. "That's it, grub on the floor like some filthy Muggle, what's your wand for, you useless sack of muck?"

[...]

"Lucky the nice man from the Ministry’s here, isn't it? Perhaps he'll take you off my hands, perhaps he doesn't mind dirty Squibs...."

[...]

"Is it true?" said Gaunt in a deadly voice, advancing a step or two toward the terrified girl. "My daughter — pure-blooded descendant of Salazar Slytherin — hankering after a filthy, dirt-veined Muggle?"

^{Half-Blood Prince Chapter 10: "The House of Gaunt"}

Answer 2

Merope’s abuse did affect her magical ability, but she did not become an Obscurial as she was raised to be proud of being a witch and abused for being a poor one, not taught to fear persecution because of it.

Dumbledore explained to Harry that Merope’s being abused did indeed have a detrimental effect on her magical abilities, since when her father and brother were both in Azkaban, she was able to use her powers better. Their treatment of her caused her powers to be weaker and less effective than they would have been otherwise.

“I think you are forgetting,’ said Dumbledore, ‘that Merope was a witch. I do not believe that her magical powers appeared to their best advantage when she was being terrorised by her father. Once Marvolo and Morfin were safely in Azkaban, once she was alone and free for the first time in her life, then, I am sure, she was able to give full rein to her abilities and to plot her escape from the desperate life she had led for eighteen years.”
_{^{- Harry Potter and the Half-Blood Prince, Chapter 10 (The House of Gaunt)}}

However, she did not become an Obscurial because she was not trying to suppress her magic to avoid persecution. She may have been afraid of Marvolo, but she was not afraid that he would hate her for being a witch, she was afraid of not being a good enough witch.

“NEWT
I met one in Sudan three months ago. There used to be more of them but they still exist. Before wizards went underground, when we were still being hunted by Muggles, young wizards and witches sometimes tried to suppress their magic to avoid persecution. Instead of learning to harness or to control their powers, they developed what was called an Obscurus.

TINA
(off JACOB’S confusion)
It’s an unstable, uncontrollable dark force that busts out and – and attacks . . . and then vanishes . . .”
_{^{- Fantastic Beasts and Where to Find Them (The Original Screenplay)}}

Marvolo clearly took pride in his lineage of wizarding ancestors, so Merope would not have any need to fear or actively and intentionally suppress her magical abilities.

“Don’t you go talking to us as if we’re dirt on your shoes! Generations of pure-bloods, wizards all – more than you can say, I don’t doubt!’

And he spat on the floor at Ogden’s feet. Morfin cackled again. Merope, huddled beside the window, her head bowed and her face hidden by her lank hair, said nothing.”
_{^{- Harry Potter and the Half-Blood Prince, Chapter 10 (The House of Gaunt)}}

She did magic in front of Marvolo and her only fear regarding magic was that she was not good enough at it for him. It’s clear that he expects her to do magic and be reasonably competent at it.

“Mr Gaunt, please!’ said Ogden in a shocked voice, as Merope, who had already picked up the pot, flushed blotchily scarlet, lost her grip on the pot again, drew her wand shakily from her pocket, pointed it at the pot and muttered a hasty, inaudible spell that caused the pot to shoot across the floor away from her, hit the opposite wall and crack in two.

Morfin let out a mad cackle of laughter. Gaunt screamed, ‘Mend it, you pointless lump, mend it!’

Merope stumbled across the room, but before she had time to raise her wand, Ogden had lifted his own and said firmly, ‘Reparo.’”
_{^{- Harry Potter and the Half-Blood Prince, Chapter 10 (The House of Gaunt)}}

Therefore, while Merope was abused and her abuse did have detrimental effects on her magical abilities, she was not subject to the specific conditions that would make her become an Obscurial.