The universe is billions of years old.

How long does an advanced civilization last? I think a lot of people make the assumption that civilizations constantly advance and that they figure out interstellar travel, so how come we haven't seen any evidence?

But what if interstellar travel is truly impossible. Heck, we aren't sure if humans can survive the radiation from a trip to Mars yet. And what if advanced civilizations only last a few hundred years before something goes wrong. We've only had radio for a little over 100 years. Honestly I'd be surprised if we are still an advanced civilization 1000 years from now. We'll destroy the planet or ourselves in warfare or the Yellowstone volcano or an asteroid will do it for us. So if an advanced civilization only lasts for, say 1000 years on average, and the universe is several billion years old, and real interstellar travel is impossible... then civilizations could have popped up for 1000 years in neighboring stars dozens of times before ours popped up, and gone away. And ours will go away before another one pops up. So searching for radio evidence is a crapshoot with really small odds. And yes, the universe is enormous but you can pretty much ignore all the other billions of galaxies because even if life exists, has existed, or will exist there, the chances of our discovering evidence of it are remote.

Narrow it down to a few million stars that are within a few thousand light years of us. Assume that advance civilization (possessing radio) only lasts for a thousand years or so when it does pop up, factor in the age of the galaxy... and there's a darn good chance there could be or have been a million different civilizations around those few million stars over the past couple billion years, but none of them happened to have their brief thousand year lifespan coinciding with ours so that receipt of their communication is even possible.