Because interstellar destructive war is easy (assuming you already have interstellar travel). Just throw rocks really fast.

Assuming hiding is technologically feasible, why take the risk?

One civilization could be at war with another and trying to hide their sources of energy.

It looks really naive that civilizations so advanced to blot out an entire star for its energy can't even find a way to co exist in such a vast universe.

But looking at how fellow humans behave with each other. I would say that is definitely a possibility.

Show me a future prediction that said we'd be using our advanced contraptions primarily for viewing porn.