What if we are? And by injecting entropy into it, we are actually hurrying (in small insignificant ways) the heat death of those universes? What if we keep going and scale out and in the future it causes a meaningful impact to that universe in a way that it's residents would be extremely unhappy with, and would want to take revenge?

What if it's already happening to our universe? And that is what black holes are? Or other cosmology concepts we don't understand?

Maybe a great filter is your inability to protect your universe from quantum technology from elsewhere in the multiverse ripping yours up?

Maybe the future of sentience isn't fighting for resources on a finite planet, or consuming the energy of stars, but fighting against other multiverses.

Maybe The Dark Forest Defence is a decision to isolate your universe from the multiverse - destroying it's ability to participate in quantum computation, but also extending it's lifespan.

(I don't believe ANY of this, but I'm just noting the fascinating science fiction storylines available)