Something to consider is that the universe is 13-odd billion years old, and from our perspective, the edge of the observable universe is about 46 billion light years away.
At interstellar distances, it is very difficult to detect something unless it is emitting something: electromagnetic energy or gravitational waves (and those are only possible to detect when there are super-massive bodies doing something extremely energetic, like two black holes or neutron stars merging).
Earth's man-made electromagnetic radius is about 110 light years. We're pretty much invisible to any other life out there.
But what about aliens that have been around for a long time? Wouldn't we see some evidence of them?
Well, the other problem is that space itself is expanding. The observable universe is 91 billion light years in diameter, but as space expands, the farthest galaxies are receding from us at ever-increasing speeds, eventually becoming invisible to us as well.
The unimaginably vast spatial and temporal scale of the universe means that countless alien civilizations may have come and gone, along with any sign of their history if their light waves are outside of our observable universe. Or their signals arrived and ceased long before humans even existed, let alone had the technological capabilities required to receive and interpret such signals (arguably, only since the advent of digital computers).
Factor in the 100 billion (or maybe 10 times more[1]) galaxies that we can see, and the 160 billion stars (solar systems, possibly) per galaxy, and the probability that we will detect an alien civilization (or vice-versa), where we are and when we are, in a universe that is mostly empty space, before we ourselves die out, seems rather small.
[1]: https://www.spacetelescope.org/news/heic1620/