There is likely to be life on some other planets. But it might only be bacteria, or the local equivalent of cows or trees. Whatever beings exist in remote regions of this galaxy or in other galaxies, they are almost certainly NOT visiting this planet.
The chances of any suitable planet developing life might not be high. Even if it does, there is absolutely no guarantee that the inhabitants will progress even to the stage of stone tools.
There is every indication that the speed of light is the absolute limit for any object that has mass.
This means that the amount of time spent in getting from one habitable planet to another could be measured in hundreds or thousands of years, perhaps even hundreds of thousands of years. While it is conceivable that an advanced race might have a life span of thousands of years, the though of a ten or hundred thousand year voyage is likely to put any one off, even an extraterrestrial enthusiast of going where no alien has gone before.
Now just supposing an advanced race of extraterrestrials has sprung up on a planet which happens to be relatively close. Somehow they detect that the Earth has life on it. Having spent a considerable time and a lot of effort getting to the Earth, these visitors then spend the next several Earth decades buzzing airlines or people on the ground, hanging around isolated areas and going beep-beep at lone travelers, farmers and kids in lover's lane.
Would you do this? Or would you land in the gardens of the Kremlin, The White House or Buckingham Palace and say "We're here!"
A few of them habitually abduct the same person many times for heaven only knows what reason The person's neighbours never notice a thing. Odd, that. Or maybe they have noticed, the abductee was always a bit odd and is getting odder.
There have been thousands of UFO reports. Most have been satisfactorily explained by known civil or military aircraft, meteorites, the planet Venus, unusual weather conditions and so forth.
Of the remainder, I'm certain that many can be put down to mistakes, ignorance, illusion, hallucination and fraud. Fraud seems to be one of the most common.
If you look at the UFO sites around the net, and the stuff that also appeared in magazines with regular UFO articles, what else do you find? Atlantis, Lemuria, astrology, conspiracy theories, the blasted Bermuda triangle, "we didn't go to the Moon" yadda t-yadda blah blah drivel snork drool; all of it loaded with unsupported assertions logical flaws and frequently, just plain lies.
When aliens finally reveal themselves, there will be nothing else in the media for the first few days, then Britney Spears will emerge over-refreshed from a party.
She will fall over, revealing some part of the Spears anatomy inadvertently. The incident will be beamed around the world and the poor old aliens will be forgotten in the furore over the glimpse of something that half the human race, maybe even all the human race has anyway.
Eventually the aliens will go away, scratching whatever passes for their heads and wondering W T H?