I think it's a mix of everything, life is likely very common, intelligent life like humans is likely very rare.

Mass extinction events happen every so many tens of millions of years so we have a limited time to advance our technology to the point where we are immune to it happening to us.

I am surprised humans haven't destroyed ourselves yet considering nuclear weapons, bioweapons and other WMD's exist.

Our technology is good but is it good enough to detect life on another planet?

The universe is unimaginably big and the distances between civilizations may be too great. I feel like our technology is only good enough to detect alien civilizations if the alien civilizations sends us a direct message with powerful equipment aimed right at us.

We haven't really been looking that long, maybe messages have already gone by. Maybe we aren't interesting enough to send messages to, maybe it's not wise to call out to darkness.

I think there are plenty of great reasons why we haven't directed alien life yet, but I am 100% confident it's out there. There are trillions of galaxies and each galaxy has hundreds of billions to trillions of stars, I just doubt we are that lucky to be the only planet with life.