Elder Guardians doesn't spawn in my survival world

i was wandering around the nether and i decided to place a portal leading to a very far coordinates, at that coordinates, i found an ocean monument and decided to loot it,
while i was looting i realized there's no elder guardian, just plain normal guardians attacking me. i tried making a new world but it seems pretty normal, theres a elder guardian,
but my specific world doesnt have an elder guardian

possible reason: if i switch back to peaceful obviously, hostile mobs will dissapear(including the elder guardian), if i switch back to normal(easy/hard) 
elder guardians wont spawn naturally