Why didn't Lúthien overthrow Morgoth?

[Nameless Thing]

She was so powerful that she managed to get a silmaril just with the help of a man and a dog. I don't think she could have killed Morgoth on the spot, but what about with the help of an army and Melian?

 

[Erestor Arcamen]

By the end of Morgoth's rein, it took an entire army and the destruction of Beleriand to do it so I really doubt that she'd have been able to take him out.

 

[Elros Tar-Minyatur]

Although Lúthien could have been instrumental in a possible ambush of Morgoth, I think she was just there to get the Silmaril to be free to love Beren. She really was just thinking about their future together and not the future of both of their races which could have been more helpful in the long run, but Beren and Lúthien were blind with love. This attaining of the Silmaril can be compared to Elrond requiring Aragorn to first win the War and become King before he could have Elrond's daughter's hand in marriage. Aragorn obviously wanted to vanquish Sauron and all his evil works, but also he knew that if he could accomplish these things he could also be with the love of his life forever. So, in the end it is not the needs of the world that come first in the minds of these lovers, but the needs of the ones they love the most.

 

[Miguel]

Although Lúthien could have been instrumental in a possible ambush of Morgoth, I think she was just there to get the Silmaril to be free to love Beren. She really was just thinking about their future together and not the future of both of their races which could have been more helpful in the long run, but Beren and Lúthien were blind with love. This attaining of the Silmaril can be compared to Elrond requiring Aragorn to first win the War and become King before he could have Elrond's daughter's hand in marriage. Aragorn obviously wanted to vanquish Sauron and all his evil works, but also he knew that if he could accomplish these things he could also be with the love of his life forever. So, in the end it is not the needs of the world that come first in the minds of these lovers, but the needs of the ones they love the most.

Beren was living A NIGHTMARE before he finds Luthien. Also, the recovering of one of the jewels proved that the Master of Lies could be tricked and punished without combat the same way he used trickery and deceit for ages. I believe this inspired Maedhros to attack him, but the attack was military and disastrous. This were really dark times, so i think Beren finding Luthien like that was a very unusual event.

 

[Aironlindo]

if Beren and Lúthien could have killed Morgoth, they would have killed him. Ainur bodies are almost impossible to destroy.Even an army cannot kill Morgoth

 

[Miguel]

Fingolfin wounded him seven times, though this is the only instance of 'fair play Morgoth:

That was the last time in those wars that he passed the doors of his stronghold, and it is said that he took not the challenge willingly; for though his might was greatest of all things in this world, alone of the Valar he knew fear. But he could not now deny the challenge before the face of his captains; for the rocks rang with the shrill music of Fingolfin's horn, and his voice came keen and clear down into the depths of Angband; and Fingolfin named Morgoth craven, and lord of slaves.

He probably didn't even need Grond or the on-blazoned shield to kill Fingolfin but this was meant to be a hand-to-hand combat duel. However, his now vulnerable body/vessel could also get killed. If Fingon had attacked Morgoth alone with an army, Morgoth would have used extra means besides Grond and his shield to overcome them, and this is excluding his servants, but this means we can only imagine based on what we know he could do.