Because of the great deeds of his past life. Great Karmas of past life lead him towards true and immense devotion to Maa Kali.
When he was appointed as priest in Maa Kali temple, he always used to think about Maa Kali. He always used to sing songs for his mother. In front of the idol of Maa Kali, he used to say - O Maa, Am i a very bad son? Why don't you give darshan to me?
Then he firmly decided to have darshan of Maa Kali. Ramakrishna ji did severe penance for 6 years and due to less sleep his eyes were always red, day and night he remembered only and only mother, but even after trying so hard , he did not get darshan of Maa Kali, due to which he was extremely pertubed.
Then, in anguish he went infront of Maa's idol and spoke to idol that if she doesn't come to give her darshan , he would end his life at that moment only. Then, seeing a sword placed in a close by room withinside the temple of Maa Kali, he ran towards it to end his life. And guess what happened?
Just before that sword was caught, the doors of the temple , walls of the temple , idol of maa kali , and the floor on which he was standing ( literally everything ) completely disappeared, as if there was nothing.
Then, he saw the huge waves of light coming from all the directions which was giving him the ultimate thrill and then Maa Kali appeared before her son. He was completely overwhelmed by this experience and his happiness was on another level, he finally got the darshan of his dear mother which he desperately wanted and was blessed forever.
- Without Maa Kali's wish, one cannot be as devoted to her as Ramakrishna was.
- Same is the case with Parmeshwar Shiv. They themselves choose their top devotees to whom they wish to give Kaivalya/Nirvana [ The Ultimate Moksha mentioned by Sri Ram in Muktika Upanishad ]
- Since Ramkrishna was a pure soul (free from lust, jealousy and hatred, obviously due to Maa’s grace) and his bhakti was on another level , he had the privilege of having direct darshan of Maa Kali.
- Maa Parvati/Kali/Lalita Tripura Sundari can be seen only by rishis (who try to fight their inner enemies like lust, greed, anger without any reason, jealousy etc.).
Such intelligent pure souls ( like Ramkrishna Paramhansa , Adi Sankaracharya , Ramana Maharishi , Goswami Tulsidas etc ) never abused any deity ( who was not their Aradhya ) in their lifetime. They never said pilgrimage related to other gods is sinful or Lord Shiva/Vishnu inferior than "deities like Vayu or Indra" because they were true scholars and gentlemen.
Unfortunately, in this Kali Yuga, such great personalities are/were abused a lot by diskCONites and andh-bhakts of a hateful cultist Madhvacharya who abused Shiv-Sakti badly ( Example : Sheshnaag or Tulsi or Vayu > Maa Durga , Maa Laxmi will kill Parmeshwar Shiv, Vayu > Parmeshwar Shiv , Parmeshwar Shiv is a sinner, Kedarnath pilgrimage is a sin etc).