Why Possible Terraformed Alien Empires in the Milky Way Might End Up Like the Islands of Oceania

The incredibly insightful animated series Kurzgesagt colorfully posited whether there are other living beings similar to human living somewhere out in the Milky Way and how these populations might or might not survive in such a hostile environment despite their undoubtedly superior technological knowledge.

What if there are thousands of alien empires in the Milky Way, each spanning a few to maybe tens of star systems, chatting, trading, sometimes shooting or ignoring each other politely? And if so, why is nobody visiting us? … What if the universe is full of life, but no matter how technologically advanced you are, space is never easy?

They use the historic example of Oceania, a chain of Pacific islands that were colonized by Polynesians. Some of the islands thrived, while others deteriorated and were abandoned.

Some 5000 years ago the first people set  out to colonise Oceania. …The Polynesians colonised them…And  although thousands of kilometers apart, even the most remote islands were connected with at least some trade and exchange….But it didn’t always work out. The extremely isolated Pitcairn islands were settled for hundreds of years and relied on trade with each other and bigger islands hundreds of kilometers away. And then the local population vanished. 

they conjecture that a similar event might take place in the vast space. That there might be a temporary terraform but it could not maintain itself, like Oceania in the long run.

There it would be relatively easy for a high tech civilization to jump from one  good star system to the next, creating connected  empires. …Then it just  may be the nature of civilization to become unsustainable or self destructive…There are numerous existential  risks, cultural, technological and environmental  that any civilization has to deal with. And smaller colonies on new planets would likely be less resilient than their homeworlds and  in bigger danger of dying out.