A new take on the Fermi paradox
TL; DR: no aliens because this is a simulation focused on one planet.
Notice how conveniently we are placed, far away from any other interesting objects in our galaxy. If you were designing a simulation, what would you do to keep your simulated beings guessing about the rest of the universe? You would make everything interesting inaccessible, and you would not attempt to simulate other species communicating, because that opens a can of worms where you now have to simulate an entire other civilization (or 3). better to just leave it empty and us wondering.
The emptiness (both physical and with respect to life and technology) is like the wall at the end of "The Truman Show" ("Free Guy", "Thirteenth Floor", "Dark City") -- the arbitrary end of our simulated universe, beyond which there is just wireframe or a painted backdrop.
I think one explanation is timescale/opportunity.
The question isn't why don't we see signs of other intelligent life? It is why don't we see signs of intelligent life within our species' technological lifetime?
Don't think of the universe as a sky full of points of light, where every civilization should be all shining at the same time. Instead I think of the universe as a vast grid of John Conway's Game of Life populated with a random scattering of 1s and 0s. Some of those patterns of cells will bloom and die out in a few generations leaving no trace. Some of those patterns will settle into small cycles but never grow into any complexity that we'd see. Some of patterns may grow into massive sprawling and seething tumults of cells for thousands of generations only to sputter and die before our cluster of cells is even born. Maybe some patterns will move across space like Life's gliders but the space is either so vast they never encounter anything or are immediately consumed by what they encounter.
Ultimately, we just might exist in conditions where the time and opportunity for civilizations to bump into each other (or even sense each other) is exceedingly rare. In some ways, that's a good thing, giving us time to develop before the unpredictable collision with other minds and cultures.
If we're inside a black hole, even if we turn everything into compute, there's not enough to figure how to leave.
Simulations runs faster than the programmers, and are more capable. Do you think we are that smart?