Good points, and I agree with a/b/c being possibilities. To add a couple others...
d) Other intelligent life already knows we're here and chooses to ignore us.
e) Faster than light travel is impossible for even the most advanced species, so exploration and finding new species is too time consuming, not worthwhile, and unproductive, and contact between intelligent species is extremely limited or perhaps non-existent.
The quietness of the universe is easily explainable (not saying it's populated and there's intelligent life everywhere, but even there was the quietness makes sense). We've only been broadcasting radio briefly, and we're already switching to digital and scrambling the vast majority of our signals. It's gonna be static if anyone listens to us. Also, if there are species that are spread across multiple star systems, they had to have found a faster communication method than radio, which means we aren't even listening or looking for the right types of signals. Perhaps the universe is extremely "noisy", but we're still examining and looking for signals that most species only use for a short time span in their development. It's arguable advanced life would be using some complex and robust multiband broadcasting that spreads across radio, uv, ir, and all visual bands... but we pretty much just look for specific frequencies because that's how WE would communicate right now. Hell, advanced species could be taking advantage of quantum entanglement to send communications. We wouldn't even begin to know how to tap into that yet.
So for me, the quietness could make complete sense. But, space could also be so vast and difficult to travel that it's not worth it to meet or travel to other species. And that would be disappointing.