A Vaishnava-based answer ahead…
Actually, if you see SriKrishna never became the king of Dwaraka. Plus, Lord Balarama, too, didn’t become the king of Dwaraka. It was Ugrasena, the father of Kamsa, who became the king. No descendant of Yadu became the sovereign ruler of the ancestral kingdom because of Yayati's curse. Even in Mathura and Dwaraka, Krishna restored Ugrasena instead of assuming the throne. The Srimad Bhagavatam and the Mahabharata both describe the following incident:
CURSE OF KING YAYATI TO YADU
- STORY OF DEVAYAANI AND YAYATI:
In the story of Chandravamsha, there came a king named Yayati. Once, he had gone to the forest, and then he found a girl fallen into a dry well. She was none other than Devayaani, the daughter of Shukracharya. It so happened that Devayaani had come with Sharmistha, the daughter of demon king Vrushaparva, for a bath. At that time, what happened is, wind blew their clothes into a pile. After bathing, accidentally, Devayaani wore Sharmishtha’s clothes. This enraged Sharmishtha, and she said, “How dare you wear my clothes? You and your father both are servants to my father; in that case, how can you wear my clothes?” and hence removed her clothes and threw Devayaani in the dry well.
But as Yayati took her out, she fell in love with him and proposed to him to marry her. But initially, Yayati disagreed and went away. Plus, Devayaani had a curse from Kacha, the son of Bruhaspatyacharya (guru of the devatas), that no brahmin would marry her. Therefore, she proposed to Yayati to marry her. Devayaani was very much angry at the behavior of Sharmistha and swore revenge against Sharmistha. Shukracharya approached Devayaani, and she narrated the whole incident. Shukracharya went to King Vrushaparva and warned him that they would leave his kingdom forever. Frightened by this, King Vrushaparva asked forgiveness from both Shukracharya and Devayaani, and in return Devayaani asked Sharmishtha to be her maid with her 100 maids. As per her demand, Sharmishtha became her maid along with her 100 maids. Shukracharya requested King Yayati to marry Devayaani, and Yayati agreed to it and married her. They lived a nice life.
2. THE SECRET MARRIAGE:
But King Yayati was attracted to Sharmishtha, who was now the maid of Devayaani. So, once in secret, Yayati approached Sharmishtha with a marriage proposal. Sharmishtha initially disagreed but then agreed, and they got married in a forest. Devayaani didn’t know any of this. Devayaani had two sons, namely Yadu and Turvasu. Whereas here, Sharmishtha too had 3 sons, namely Druhyu, Anu, and Puru. Now, once Yayati and Devayaani were roaming in the forest, the kids of Sharmishtha came and called Yayati ‘father’.
3. CURSE OF SHUKRACHARYA:
This made Devayaani doubt Yayati as to why these kids were calling him father. As she got to know the truth that Yayati married Sharmishtha in secret, she went to Shukracharya and complained to him about Yayati. Enraged by this, Shukracharya cursed Yayati to obtain old age.
Shukracharya said, “If someone agrees to take your old age, then you can transfer the old age to them and can even receive the old age back if you want.” At this, Yayati approached five of his sons - Yadu, Turvasu, Druhyu, Anu, and Puru, asking whether they would accept his old age. Yadu denied taking the old age; therefore, Yayati cursed Yadu that his descendants would never rule the kingdom. The same happened with Turvasu, Druhyu, and Anu.
Finally, the youngest son, Puru, agreed to accept old age, and hence, Yayati blessed him and said that his descendants would rule the kingdom in the future. Thus, his old age was transferred to Puru, and Yayati took his young age and enjoyed his life with Sharmishtha and Devayaani and then re-transfered the young age to Puru and took away the old age back and went to forest for meditating of Lord Srihari with his wives and finally reached Srihari’s Supreme abode.
WHY DIDN’T KRISHNA OR BALARAMA BECOME THE KING?
So, in this story, Yadu, the son of Yayati, was cursed by Yayati; that's why none of his descendants could rule the kingdom. Krishna too appeared in Yaduvamsha; that’s why He too respected Yayati’s curse and didn’t rule Dwaraka, but made Ugrasena rule Dwaraka in a dharmic way. After killing Kamsa, Krishna didn’t become king but became a kingmaker. Wherever He went, He made kings. He went to Mathura, killed Kamsa, and made Ugrasena the king. He went to Magadha, made Bheemasena kill Jarasandha, and made his son Sahadeva the king. He went to Pragjyotishpura and killed Narakasura and made Bhagadatta the king. After making the Pandavas win the Mahabharata, Krishna made Yudhishthira the king. Like this, He killed the unrighteous king and made the righteous people the king.
Thus, Krishna’s main role was not being the king; Krishna didn’t have any desire to become the king. His main aim was to re-establish the Dharma, which is evident from the Bhagavad Gita itself when He says, “Dharmasamsthaapanaarthaya sambhavaami yuge yuge”. In His Ramavatara, He killed Ravana and became the king of Ayodhya and ruled it for about 11,000 years. But in Krishnavatara, the same Rama Himself became the kingmaker, rather than the king. Though Krishna is unaffected by any curse, because He is the Supreme Lord Vishnu Himself, He respected the curse of Yayati. Yet He is known as Dwarakadheesha. As the Ishavasya Upanishad says, ‘Ishavasyamidam sarvam, ’ everything belongs to Krishna. Krishna is Jagannatha Himself: the Lord of the entire universe. If the whole universe belongs to Him, then how can Dwaraka be excluded? Therefore, Krishna is the true king of Dwaraka, though Ugrasena occupied the royal throne and ruled under SriKrishna's guidance.
Therefore, He is the true Dwarakadheesha. Jay Jay Dwarakadheesha SriBhaishmi-Bhama-Vallabha SriKrishna Paramatma!!!🙏🙏😊✨
Hope this helps!
Jay SriRam!
ShriKrishnarpanamastu!