Actually, if you look, even before Rukmini, Krishna had married Neela. Neela was the daughter of Yashoda’s brother Kumbhaka. She had done penance in her past life to marry Krishna and be His first wife, even before Krishna’s upanayana, or thread ceremony. As the fruit of that, Neela was born as the daughter of Kumbhaka and married Krishna. So, Krishna married her. She had the presence of Lakshmidevi within her. So, that’s why Krishna married her in Vrindavana.
The unmarried Gopikas had also done Katyayani Vrata to get Krishna as their husband. And as per Goddess Katyayani and Krishna’s grace, Krishna married all the Gopikas who did the Katyayani Vrata. These Gopikas too had the presence of Lakshmidevi within them, and hence Krishna married them. After that, when Krishna killed Kamsa, and after His upanayana and studying under Sage Sandeepani, and defeating Jarasandha 18 times, and while living in Dwaraka, He married Rukmini.
Rukmini Devi is Saakshaat Mahalakshmi Devi. There is no difference between Rukmini Devi and Mahalakshmi Devi. You can understand Saakshaat Mahalakshmi and Lakshmi Sannidhana by this example. For example, you have an idol of Lakshmidevi with you. Now, that idol itself is not Lakshmidevi, because it is an idol. But Lakshmidevi’s presence is there in that idol. The same case is with the Gopikas and the other queens of Dwaraka, except Rukmini and Satyabhama. They all have the presence of Lakshmidevi within them and are not Lakshmidevi themselves. Whereas Saakshaat Lakshmidevi means Lakshmidevi Herself, and not a different personality having Lakshmidevi within Her.
Satyabhama is Lakshmi Herself. And there is no difference between Mahalakshmidevi and Satyabhama Devi. Both are the same. Rukmini is Sridevi, whereas Satyabhama is Bhudevi. As Sridevi, She is the presiding deity for Sattva Guna. Therefore, as Rukmini, She showed devotion and surrender towards Krishna. Whereas, as Bhudevi, being the presiding deity of Rajoguna, She as Satyabhama, showed playful pranaya kalaha and devotion towards Krishna. Though She doesn’t have anything like dvesha or jealousy, Satyabhama Devi acted like that, contributing to Krishna leela.
If Rukmini and Satyabhama are directly Mahalakshmidevi, then why did Krishna marry the Gopikas and the other 16,100 + 6 more queens? These queens of Dwaraka, except Rukmini and Satyabhama, were Agni putras and had done penance to get Krishna as their husband. That’s why they were all born as women with the sannidhana of Mahalakshmidevi within them, and then Krishna married them. The Neela Devi, which I discussed earlier, then merged into Nagnajiti (also known as Neela), who is one of the six main wives of Krishna (known as Shanmahishis). These Shanmahishis after Rukmini and Satyabhama, are basically Jambavati, Kalindi, Bhadra, Neela or Nagnajiti, Mitravinda, and Lakshana. Out of these too, Jambavati had the maximum presence of Lakshmidevi within Her. So, this Neela of Vrindavana merged within this Neela or Nagnajiti of Dwaraka.
And talking about the Gopikas, these Gopikas were Apsara Strees who had done penance to get the contact of Krishna. These Apsara Strees worship Bhagavan Vishnu as their husband. And when they have Lakshmi sannidhana within them, Lord Vishnu accepts them as His wives. So, Apsaras were born as Gopikas and had Lakshmi sannidhana within them. Therefore, Krishna married all those unmarried Gopikas who had done Katyayani Vrata. Krishna is always Ekapatnivratasta; that is, He doesn’t touch any woman other than Lakshmidevi.
But among these Gopikas and the Dwaraka queens too, it was Lakshmi only who was among them and was experiencing the joy given by Krishna to them. So, it is Krishna doing kreeda with Lakshmidevi only among all of them. Krishna is Anaadi Brahmachaari and doesn’t need anyone for His ananda. He doesn’t even need Lakshmidevi for His ananda. He is svaramana and is full of pure and unadulterated joy within Himself.
It is He who gives the joy to Lakshmidevi, and that’s why He is known by the name Eesha. So, for marrying Krishna, it must be Saakshaat Mahalakshmidevi Herself, or She should have the sannidhana of Lakshmidevi within Her. Or else, Krishna won’t even touch Her. Not only for marrying; even if you are offering something to Krishna, it should also have Lakshmi sannidhana. Or else Krishna won’t accept it. That’s why we put Tulasi on the bhog we offer to Krishna, because Tulasi is Lakshmidevi Herself.
Lakshmidevi, as Durgadevi, also participated in the Krishnavatara. She was born as the daughter of Yashoda and Nandgopa (that’s why She is known as Nandagopa Kulodbhave and Gopendrasya anuje). She was taken by Vasudeva, and then, when Kamsa tried to kill the baby, She showed Her ashtabhuja form and warned Kamsa that his death had taken birth somewhere else. When Arjuna was fighting the Mahabharata Yuddha, in the front there was Krishna Himself, driving the chariot. At the flagpost, there was Hanumanji, who was protecting Arjuna. But at the backside of the chariot there was Durgadevi protecting Arjuna. So, in the Krishnavatara, Lakshmidevi participated in three of Her forms: Sri (Rukmini), Bhu (Satyabhama), and Durgadevi (in the Kurukshetra war).
Hope this helps!
Jay SriRam!
ShriKrishnarpanamastu!