I'm simply observing any Big Bang model accepts a huge influx of very dense energy that rapidly expands or inflates - affecting spacetime around it rather drastically
It isn't affecting spacetime around it, the BB is spacetime.
- and asking why must spacetime be created by that event rather than just be affected by it.
Because it's a function of the model. I don't know specifically what part of the mathematics of the model is linked to that assumption, but I was always under the impression that it is a fundamental element of the model. I don't think you can alter that assumption without changing the model so much that it would (be radically different) require a new name, like the Little Bang or something.
Rosborne979 - no again that's another random connection that has no correlation to the simple question I asked. I am puzzled you seem inable to comprehend such a simple question and preferred to randomly respond to other rather simple questions I didn't ask.
Because I'm not as smart as you are, but I'm doing my best to answer the question based on my understanding of things. It's not like you're asking me what I had for breakfast. You're asking some obscure question about core cosmological assumptions.