There were also Giants. What changed?

The 13 families were part of the group that survived in caves and tunnels underground during the deluge. They had saved tech, mystical knowledge and wealth.
Once the waters receded, they implemented ways of killing off non bloodliners at an earlier age.
It would be like killing a tadpole before it becomes a frog- they kill us with cancer, drugs you name it- before we evolve to the next level of our evolution or enlightenment. Until now.

I've heard that 13 bloodline known families are just a lower class/servants of a higher class. They are just exposed to public. Look here, not there kind a thing.

That is a fact- to give example, look at the grey and black popes.
The name Orsini appears. There is a whole level of black magicians above the 13. So yes, you are correct, I have seen the list, but do not have immediate access to it right now.
"They" call the United States the new Atlantis. Manly P Hall and other occultists wrote extensively about it.

If people knew the whole truth, they wouldn't believe it - not now, it's too soon. What did "they" use, for example, ravens and other matters ..., "communication" through the astral, etc.
The bubble in which society was brought up is more fiction and what was considered fiction is true.