There have been other similar questions, but none of the answers address this point.
- Inflation ends after the first 10^-32 seconds. Our observable universe was the size of a grain of sand that contained a mass-energy ~10^80 GeV, which is much denser than the critical density that would presumably make it collapse into a black hole.
- since the mass-energy in the universe was evenly distributed at the end of inflation, there was no over-density in one region that resulted in black hole. This can be explained by Newton's shell theorem.
- separately, radiation exerted an outward pressure that prevented over-dense regions from forming. Newtonian dynamics goes a long way towards explaining how the outward pressure of radiation balanced the collapsing force of gravity.
However, it seems to me that if the observable universe was all there was (just a 10^80 GeV grain of sand surrounded by vaccuum), then the universe would have collapsed to a black hole. The universe must have been much larger than our observable grain of sand, and mass-energy must have been smoothly distributed outside of our observable grain of sand.