It seems like the obvious answer is that no-one is enveloping galaxies in Dyson spheres. As Dyson says at the end of the article: "The failure of one guess does not mean that we should stop looking for aliens."
The Dyson sphere is really just the extrapolation of 1950s USA - maximize comsumption, ignore pollution, expand at all costs.
There are other extrapolations. Humans put their minds in computers -> people need more and more computing power to do the things they want to do -> all available matter is turned into processors -> energy is need to run them all. They only thing limited humans at that point is matter for processors and energy to run them. Everything else is pointless.
That has nothing to do with "maximize comsumption, ignore pollution, expand at all costs."
This is exactly "maximize consumption, ignore pollution, expand at all costs". When you decide that your use of energy / matter transcends all other purposes (including the evolution of other life) then exactly what are your priorities?
Precisely. The only thing this study tells us is that no galactic-scale civilization in the 100 or so closest galaxies fits the pattern imagined by the America of the 1950s. I find that strangely reassuring.
> maximize comsumption, ignore pollution, expand at all costs
Exactly this. I don't think a supercivilization would emerge as one with this maxim. It would die in its own cradle. Likewise, I believe our problems of this nature must be solved here, at home, before moving out and spreading our tragic narrative elsewhere.
What if the smart cultures have realized the best way is to live quietly, sustainably in balance with nature on their planets. This might well mean not expending the vast energy needed to go to space. Perhaps also they are comfortable with themselves and do not need to seek out everyone else.
The Dyson sphere is really just the extrapolation of 1950s USA - maximize comsumption, ignore pollution, expand at all costs.