It comes from simply being the way that black holes work, I'm surprised you don't know this. Nothing can ever reach an event horizon from any frame external to the event horizon and this is not a disputed fact, it's universally accepted black hole physics.
Time dilation, length contraction and redshift all approach infinity from a distant frame as an object approaches the event horizon, so obviously this means that there is never a time on a distant watch when it's too late for a falling object to accelerate away from the black hole.
If red shift approaches infinity its energy approaches zero and it ceases to exist to the observer. Does that help
Edited by Flummoxed, 14 September 2019 - 04:52 AM.