Why is it so hard for mankind to figure out if there is really "intelligent" life on another planet?

The ingredients for creating life spreads thru out the universe. It spread like the common cold and has done so for billions of years. Time trumps distance.

If it land on an earth like planet crap happens.

Why can't you thrive off of ionizing radiation, and use it as food?  Other life can do that.

Besides that, how do you know other life hasn't sent messages to this planet already?  Do you know what would happen if the universe is all of the sudden not god built?  There's a lot of bad stuff that would happen if religion was revealed to be the lie that it is.  How do you know our 'leaders' don't know this, and work to keep the people from knowing.  Why do you think people who claim to witness or otherwise know about alien life existing are quickly ID'd as crazy?

THEY might be at a PRE RADIO stage of development OR WE might be FAR behind them in terms of more advanced communication technology we are not listening for----Remember, our respective civilizations, if any started at different times  and with different histories.   

In case you haven't heard:  The universe is a big place.

were not smart enough yet .

You misspelled inteligent.

Yes, that's the Fermi Paradox and a lot of work has been done on it.  There are various opinions:

* We're the first, but there will be others in the future.

* Planets which can support life are very rare.

* There are filters which prevent life from reaching that stage, such as natural disasters or dangerous technology which causes extinction.

* There's a fair amount of intelligent life in the Universe but it doesn't call attention to itself because there's a powerful hostile species which they're all trying to hide from.

* We're in a zoo and signals are blocked.

* The kind of signals we can detect are only produced for a very short period of time in a civilisation's history.

* Alien life is so unlike us that it isn't recognisable or doesn't go into space at all.

* It takes too much energy.

There are various others.

because there are no planets - we live in a self-contained closed system with no means of ingress or egress and there are no planets, there's no outer space, and we need to start caring about each other and the world we live in because there's no place else to go and no one to help us.  

This is the Fermi Paradox. Where are all the aliens? There are many possible answers, but nobody knows which, if any, are right. 

Lots of possibilities...

First - We might be the only intelligence there is.   I don't think so, but... it's possible. 

Second - We might be one of many intelligent species, but *we* are the most advanced.  

Third - it's possible that intelligence is out there, but very rare, and very far apart.  If that's the case, there may not have been enough *time* for our signals (or their's) to have reached one another yet. 

Fourth - it's possible that intelligence is common - but they've refrained from contacting us because they know we're not ready yet. 

Fifth - maybe they know about us, they want our planet, but won't be here for another month or so...