He does that because Madara knew that after losing his love, Obito would lose hope in true peace and follow Madara's plan. Madara's actual plan was to become the ten tailed jinchuriki and cast infinite tsukiyomi, after being revived. Obito's plan was also to revive Madara by using Nagato..
Correspondingly, why did obito help Madara?
Originally Answered: Why did Obito helped Itachi to slaughter Uchiha clan? To weaken Konoha and limit the number of people who could have caught his bluff over being Madara.
Secondly, did obito revive Madara? Mortally wounded by Minato, Obito becomes the Ten Tails host and is defeated by Naruto and Sasuke with the support of the Allied Shinobi Forces. A guilty Obito tries to redeem himself by reviving everyone who died in the war, only to be possessed by Black Zetsu and forced to resurrect Madara instead.
Subsequently, one may also ask, why did Madara act like Tobi?
So his identity as Obito was out of question. Being the hidden leader of Akatsuki, the only reason he joined as Tobi was to keep a check on members and carry out the plan as soon as possible. Itachi knew him as Madara and when he entered Akatsuki as Tobi, it made Itachi even more suspicious of him.
Why does obito call himself Madara?
When we first meet Obito up until Itachi dies, he calls himself Tobi. Events before his onscreen intro and after Itachi's death, he is called Madara. He is referred to Obito after his mask is broken during the war and when he was a genin with Kakashi and Minato.
Related Question Answers
What age did Itachi die?
21 year
Is pain an Uchiha?
A descendant of the Uzumaki clan like Naruto, Nagato's Rinnegan is later revealed to have belonged to Madara Uchiha, who transplanted his eyes into the child as part of his plan. For this, Nagato adopts the name of "Pain" and kills Hanzo, taking over as the new leader of Amegakure and becoming a "god" for its citizens.Who killed Itachi's team?
Tobi
Who was Itachi's best friend?
Shisui Uchiha
Who killed shisui?
In the novel, Shisui was attacked by Danzō and Sugaru from the Aburame clan, whose insects poisoned Shisui. In the anime, Danzō arranged a meeting with Shisui and stole his eye after a small scuffle. In the "The Two Uchiha" story, Danzō and Root ambushed Shisui and put him into a corner until Itachi came to his rescue.Which Kage did Itachi kill?
There actually are simple He never killed a Kage. He defeated the Third Mizukage in battle but defeat is not the same as kill.How old was Kakashi when Minato died?
Kakashi became a Genin at the age of 5 and Chunin at 6. Obito became a Genin at the age of 9 and Chunin at the age of 11. It was around the time when Obito became Chunin that Kakashi was promoted to Jonin. Obito then "died" at the age of 13, which was almost two years after his promotion to Chunin.Who killed Madara?
Madara was never killed by anyone in his first life. Madara used the rinnegan to revive himself and achieved the powers of the sage of the six paths. when he was giving Naruto and Sasuke a tough time, Zetsu put his hand through Madara's heart landing a fatal blow which later caused his death.Is obito stronger than Madara?
Obito has two Sharingan and, since he's transplanting them into himself, they gain his Mangekyo. Which means Obito is stronger than Itachi with both eyes but gets his ass handed to him by Black Zetsu but Itachi can beat Madara. Here's how little sense this makes: Black Zetsu>Obito>Itachi>Madara.Who is the fake Madara?
Obito
Why is Tobi evil?
Well the reason why Obito became evil is because of Rin Nohara the girl he loved died even though Kakashi promised Obito that he would protect her before when he died in 3rd great ninja war. well that's what everyone thought at first because he didn't return to the hidden leaf when he was saved by Madara.How did obito get rinnegan?
He implanted the left Rinnegan into his being but he had hidden the right Rinnegan. Nagato, being of Uzumaki lineage, is able to wield the Rinnegan because of his life force and chakra reserves. Obito on the other hand, doesn't possess large enough chakra reserves to handle both Rinnegan at the same time.Why does Tobi wear a mask?
Madara told Obito/Tobi to use his identity until he is revived. Since he used Madara's identity, he had to wear a mask, otherwise some may had revealed that he isn't Madara. Found in this Wiki on chapter "Moving the Plan Forward" and from Chapter 606 in the Manga.Why does obito pretend to Tobi?
So his identity as Obito was out of question. Being the hidden leader of Akatsuki, the only reason he joined as Tobi was to keep a check on members and carry out the plan as soon as possible.Is Tobi actually Madara?
Jason Thompson of Anime News Network was shocked when he learned that Tobi was the real leader of Akatsuki (rather than Pain) and when Tobi refers to himself as Madara Uchiha.Who kills obito?
Obito Uchiha is not killed by anyone. After seeing that even with the combined efforts of Naruto and Sasuke, Kaguya was far from defeat he scarified his life in order to give his Sharingan to Kakashi . After this Kakshi was able to manifest a full Susanoo and helped Naruto and Sasuke in fighting Kaguya and kill her.How did obito sound like Madara?
It was never stated how Obito made himself sound like Madara but he could've. Obito did the same by deepening his voice and having his voice similar to Madara's because he was the very few people alive that knew Madara's voice.Did Nagato revive Jiraiya?
Nagato converts the corpse of a Rain kunoichi named Ajisai (????, Ajisai) into a new Animal Path before beginning his attack on Konohagakure. The rest of the Paths are destroyed in the fight against Naruto, with the Deva Path disabled, and Nagato recovers his faith in Jiraiya and world peace while talking with Naruto.Why does Kakashi kill Rin?
Rin requests Kakashi to kill her so she may not be used by the Hidden Mist ninja as part of a Trojan Horse scheme against Konoha, but Kakashi is reluctant. She eventually forces herself on the way of Kakashi's Lightning Blade that he originally directed at the pursuing Hidden Mist ninja, killing her. 
