I just imagine an intelligent beaver: "There can't be any other intelligence out there, just look at all these rivers and streams!"
Meanwhile, humans are enjoying fusion-power and will take a little while to notice suspiciously-well-engineered beaver dams showing up everywhere.
The argument is really more why is there only one technological species on the planet - the answer is the first one to arise will displace all the other potential competitors. This is exactly what has happened on Earth and why any other species that has a chance of creating a technological civilisation is not doing so well.
The same argument applies to the universe where the first civilisation that chooses to take over the universe will displace any competitors that choose not to. All it takes is one civilisation to spread and the whole universe goes dark.
Orang-Utan: 50,000
Chimpanzee: 200,000
Bonobo: 35,000
Homo Neandertalensis: 0
Homo Habilis: 0
Gorilla: 100,000
Homo Sapiens: 7,500,000,000
Note that ants don't directly compete for a niche with humans.
And megacolony species such as the Argentine ant are displacing other ant species.
2. Ant biomass is about the same as human biomass on Earth.
3. Typical human mass is 60kg, typical ant mass is 3mg.
4. Do the math.
Arguing that smelting steel is the key thing is the typical, we're good at this therefore this is what matters argument we've been making since time immemorial.
Humans can't sneak into other organism's bodies and take over their DNA (yet, to be sure) but viruses can, so humans just don't have a real shot.
Could you please explain that to the World Bank and governments in Africa, SE Asia, China, and Oceania that insist on damning the last free-flowing rivers on Earth?
When it comes to hydroelectric power and titanic concrete structures, we look for very different water-situations than beavers do.
In order to justify ignoring all the burning stars, it needs to be easier to tap than solar and much much more energy than all the stars will ever generate. I think that requires new physics.
Really the energy source must be infinite. If you can see that it will run out in a trillion years and you can survive for another billion by harvesting suns, somebody will.
We have nuclear power but still dam rivers, and I think beavers notice.
OTOH If there is a source of unlimited free energy, maybe some of those bright spots in space aren't stars at all.
Even if we move onto mars a GRB would cook all of us.
And even if it's something considerably more boring then expanding to other planets or even star systems might not save a civilization from collapsing.