The window for civilisations to develop and become advanced enough to travel space is very small.
Man has been on Earth 500,000 years give or take. It's only in the last 60 years that we have had technology to leave Earth in any for and we still regard getting to Mars a major under taking.
The science required to fly to another sun and it's planets is beyond us and
Alpha Centauri is 4.22 light-years from Earth. And there's nothing on the planets that shows signs of life.
The massive investment it takes to fly the universe would bankrupt the Earth and any civilisation that can afford it will be advanced to the point that will probably kill their planet like we are doing now. But assuming some civilisation has managed to get to this point they will want a return on their investment and will be here to exploit what we have. Not taking random flybys on aircraft, visiting dirt farmers and yokels here.
A more logical explanation is this is top secret military stuff and nothing more. The military is well capable of putting out the info.