TLDR: We're technologically way beyond accepted science would have us believe and so are many of the civilizations 'out there' - society is engineered to keep the masses in a very narrow band of accepted science.
Using the explanation that space is so vast and that it would take any other civilization lifetimes to even reach us - as already mentioned - is only looking at things from the (currently disclosed) perceived limits of accepted science.
It's the equivalent of someone in the past where the height of technology was the sailing ship disbelieving that travelling the Atlantic could occur in mere hours, simply because it's beyond the limits of technology at that time.
Quantum Entanglement is a good example of science starting to get onto the right track; once they start looking more into how consciousness affects matter and what's beyond what we perceive as physical then we'll be getting somewhere and what we perceive as vast distances really aren't an issue.
Do we honestly believe that what NASA shows us is the pinnacle of what the Human race after all these years has managed to come up with in terms of space travel? Let's be honest, current space tech is a variation of an over-sized firework that fights against mavity to leave the atmosphere.
I think most people probably expect there are some secret programs (such as with the stealth bomber) that are years ahead of what we know of but it goes way beyond that - there's evidence various organisations/corporations came across anti-mavity (not strictly the right term but let's run with it) as far back as the 1950s, if not earlier, before reports on those early discoveries went into black projects when they realised what the implications were of revealing this sort of information.
This is just us, now multiply that by how many other planets, solar systems, galaxies and dimensions are out there.
As to why we're apparently not visited; well we are, but you try convincing someone of that when they've been brain washed all their lives to believe we're alone and anyone who says otherwise is a nut or a conspiracy theorist; a CIA invented term to discredit anyone who challenges the accepted story - they sure did a good job there eh, let the masses do the work for you, brilliant.
