A Dyson sphere around a black hole

Why do we think Dyson spheres exist. It's completely conjecture.

Exactly my thinking every time I read about them. It's one idea thought up by one scientist. It's so human of us to think some advanced race would build a giant capture device around a star... did anyone stop to ask that if a civilization could do that, they would likely already have technology that could (to our eyes) generate power out of thin air? Nope, caveman brain build big wall around star to get ALL power!

There are other benefits.

The internal surface area of a sphere with radius 1AU has so much area that its unlikely any spacefaring civilization would ever spread to that many planets. It would be enough to have billions of versions of your civilization/species with room to spare, AND have them all be able to communicate without light years of transmission delays, never mind time and cost of travel, and thus drift apart. Then, one has the opportunity to otherwise live in very similar circumstances as the planet one evolved on. Looking at our attraction to nature I would guess any species would think of this as a benefit, and would prefer it over terraforming faraway hostile environments or inhabiting cramped space cabins.

So yes, if you have the ability to make a Dyson sphere, I can very well imagine that you would.

What if by the time you get to that level of technology, you no longer need that much physical space? I don't even mean in a soft sci-fi "evolutionary progress means becoming energy beings", I mean a hard sci-fi "advanced civilizations just digitize themselves into a virtual reality simulations."