Igloos, desert pyramids, jungle temples, witch hut's, shipwrecks and underwater ruins spawn at superflat world

I just wanted to create a clear superflat world with overworld preset with only villages, after deleting everything else only keeping villages the world is generating also structures that shouldn't be there like shipwrecks, underwater ruins, igloos, desert pyramids and jungle temples started to spawn there. The biome was set to plains.