Why don't Extraterrestrials reveal themselves?

Maybe their home is a relatively close by solar system and they are not necessarily too much more advanced technologically than ourselves. If they came from much greater distances then they would most definitely be 'light-years' more advanced than us, excuse the pun!

And they do not want to reveal themselves to us now because as they observe the technological progress of mankind they realise that we will reach a comparable technological standard as themselves, or even surpassing them, in the near future. And from observing the apparently destructive nature and mind-set of mankind they fear us and fear what we may do to them in the future if they were to initiate contact.

In fact maybe we are more advanced militarily than they are right now, perhaps weapons are a thing of the past in their civilization. So they are left with a number of choices. They can either destroy us now which may not be in their nature or may not be within their capability or they can remain anonymous as much as possible while still keeping a close eye on us, perhaps watching our rapid technological progress with growing concern.

Perhaps they stumbled across planet Earth only two or three thousand years ago. If their space travel technology then wasn't that much more advanced than our own current technology then maybe the spaceships of Ezekiel would make sense. Maybe as the years went by their technology advanced and by the middle of our 20th century they had devices such as Foo Fighters carrying out their surveillance. Perhaps this was a wise idea as their spaceships had a tendency to crash into deserts. In the 1970s they were advanced enough to monitor our own admirable achievements in space and to easily out manoeuvre our own spacecraft.

Is there any correlation between UFO records throughout the ages and improvements in the technology of these UFOs? For a technology not much more advanced than ourselves there should be tell-tale signs. Has anyone out there any work done on this? Could the sightings in biblical times correspond to our technology in say 2050? And late 20th century sightings correspond to our technology in 2100. But why would it take them over 2000 years to develop what we could/will do in 50 years? Maybe we have an advantage of reverse engineering that they didn't have. Or maybe we are 'smarter' or have greater capacity for rapidly increasing our technologies than they have.

Imagine if we had focused on the space race instead of the arms race. How much more advanced we would be in terms of exploring our solar system. We would surely have walked on Mars by the 1990s. We would at this stage perhaps be planning for exploring other planets in nearby solar systems or even on route to these planets (though maybe that's a bit ambitious). Then again maybe there is truth to the argument that nothing advances us more technologically than big spending military departments, this is just a maybe!