Not much room for grain storage inside.
Also, they took 30 years to build. Can you imagine spending 30 years on a food storage unit?
Also, can you imagine a non-Pharaoh commanding the resources necessary to build them?
The bible story has Joseph winning his way into the Pharoah’s confidence, and that twice (the first time he got detoured into the dungeon by a scheming, lying woman but a godly man could not be kept down).
To the point that if Joseph had WANTED a pyramid for the purpose he would have been granted authority to get it built. The massive stone edifice would have guarded the grain against temperature variations, for one thing.
However it is dubious, very dubious, based on the bible account. These storehouses were built in cities. Doubtless Joseph saw no point in wasting efforts for facilities that weren’t intended for show, and we don’t find any city located pyramids today. Maybe archaeologists may turn up some of these storehouses in the future, identifying positively what they were.
The time line would be too long for the time line of the “7 year warning” of Joseph’s dream, unless there were expedients we know nothing about today.
Hollowing out an existing pyramid might have been easier, a repurposing, and maybe Joseph might have suggested this if it made sense... but again, volume calculations.
And, I assume we have now gotten X-ray imagery maps of all extant pyramids and found none that were seriously hollowed out.
In a “sanctified imagination” in connection with standard Christology, an edifice that had been intended for a burial being repurposed to serve the means of life and survival wouldn’t be utterly absurd from a religious point of view. But if it were that important, one might think it would have shown up in the bible. It just seems very dubious. Carson had to learn enough science to be a doctor. You don’t estimate the blood volume of a man at more than what his whole body displaces.
There is some speculation that the chamber(s) were used for grain storage. Whatever. The fact that you would take Carson’s theory about this so seriously is an indication of shallowness; the same that attends to low-information, knee jerk voters.