To understand how this could be, you have to be able to realize what life is like on other planets. Just like in our oceans or on land masses, there are an infinite number of life forms in all shapes and sizes. Outer space is basically a mirror image of this in that there are an infinite number of life forms in all shapes and sizes.
There are three (3) concepts that Earthlings simply do not understand or are not easily convinced it is possible and are least likely to believe it without physical proof and corroboration at the highest levels.
(Humanoid Extra Terrestrials are referred to as HET)
1. HET exist on other planets and have been present on Earth the whole time life has been present here.
2. HET don't die, just their bodies die. They essentially live forever, as long as they can maintain the respective system each group resides in.
3. HET are militaristic in nature.
1. HET exist on other planets and have been present on Earth the whole time life has been present here. What this basically means is that there are humanoid life forms on other planets as well. So if one of these life forms was present on Earth, they would simply appear as an Earthling unless they were to reveal the truth about themselves. Most Earthlings are not aware of this or simply do not want to believe it, so they continue to search for ET in some other foreign form they could distinguish easily from Earthling. In addition, most people don't have the time or energy to pursue an understanding of this, so they simply rely on the government or military to keep them informed, as if they would never keep something like this from them.
2. HET don't die, just their bodies die. They essentially live forever, as long as they can maintain the respective system each group resides in. Another aspect of life on other planets Earthlings have a difficult time with is the concept that beings don't die. Their bodies die, but the being itself (whether you want to use the concept of a spirit, etc...) can be ported into a new body and they continue to exist. You might think of the body as a rent- a-car and they just keep exchanging them as they go on throughout life. So on other planets, the concept of dying is as foreign to them as the concept of living forever is to an Earthling. Their bigger problem is not dying individually, but failing to keep their system surviving and failing to exist as a group.
3. HET are militaristic in nature. This is the most difficult area for Earthings to grasp because there are no examples on Earth to compare it to interms of how Human societies are run. In addition most people want to believe in "good' and think of optimistic outcomes. Thinking of the possibility that ET would be of "bad" nature and that there is no hope is simply to difficult for the Earthling mind to process.
With these three basic concepts in place, you can then formulate an understanding of what is going on. ET, by their militaristic nature, want slaves to do their work for them. By creating prisoners (of war), planets, and placing the beings on them in their humanoid form, the HET (part of the ET) can live among them on Earth, appearing as Earthlings, allowing for complete control of the planet and the beings on it without the Earthlings having even the slightest clue as to what is going on. In addition, by being able to morph and polymorph themselves when they appear to die on Earth, they can continue to live here and rule there, as the Earthlings only get to see life for a brief, maybe, 100 year period at the most, and cannot comprehend life spanning more than that, much less the 4.5 billion years Earth has been in existence or epochs even longer than that.
So when you fast forward to modern day reality, you can see the Earthlings as a whole are beginning to grasp the concept that ET and UFOs might exist. What they are completely naive to is that society controlled by HET's is intentionally subliminally putting out this information, helping the Earthlings to become aware, all the while using terms like ET and UFO, instead of HET and Volutes, so the Earthlings will focus there attention outer space, not Earth, and works like UFO, which are technically incorrect, and will further prevent them from figuring out what is happening.