And why not?

I think the old balloon analogy of the universe can be applied to black holes. If one makes a pucker in the surface of a balloon and gives it a twist trapping some air inside, that would be similar to the formation of a black hole. We observers on the (spacetime) surface of the balloon see only the highly distorted (curved spacetime) rubber skin left behind but we don't see where the missing part of our (spacetime) rubber skin has gone. It has gone into the black hole which is a mini-balloon universe of its own.

The alternative to a finite spacetime is an infinite spacetime and I pick the former rather than the latter.Changes in spacetime are distributed universe wide so any local effects would be negligible. Think of it this way. The spacetime condition of a universe with few or no black holes should not be the same as a similar sized universe made up of an enormous number of black holes or even a few really large black holes. I can't imagine that black hole formation leaves the rest of spacetime unchanged. Changes in spacetime are distributed universe wide so any local effects would be negligible.Where does one get more spacetime? I understand the expansion of space to be a change where spacetime goes from a highly curved condition to a less curved condition. In other words, existing spacetime is being "stretched" out but no new spacetime is being created. There is no such thing as more spacetime coming from elsewhere or "replenishing" spacetime that is lost.

Black hole formation converts normal, weakly curved spactime into highly curved spacetime thereby stretchingthe space that remains on our side of the Schwartzschild radius and this could contribute to the appearance of expanding space.