As far as I know...NO one has established the end-purpose of the Pyramids. No, it’s not a proven science or proven history item....so anyone can still say more or less what they desire.
I will admit, for grain-silo purposes....it’s a marginal one-star possibility. Generally, you’d want a place where it’s near the fields, and this really doesn’t fit the requirement.
Face it. I don't know who propped up Dr. Carson as a candidate. Except for when he's in his area of expertise, brain surgery, his facts aren't real factual.
It is also entirely possible that the pyramids were built for one purpose and eventually ended up being used for something different.
I've seen art galleries which were originally built as churches and trails built for the original purpose of moving British troops into what is now the Pittsburgh area paved over to become highways and turnpikes.
I have been to the pyramids.
I have been in the pyramids.
The “grain storage” space available in even the largest pyramids would equal 2-3 semi trailers ... certainly not enough to feed a culture for 7 years ... heck, not enough to feed the workers that built the pyramids for a week. Maybe not even a day.
The reason you see, they pyramids are solid rock. They have a couple (usually 2 functional and maybe 2 traps) of stairwells and air vents, and then 2 rooms that are about 6 feet tall and maybe 30 x 30 down inside. There are no lights, and no fans to blow air in, and they are extremely hot and humid (relative to outside) ... not what you would want for grain storage.
Anyone promoting the pyramids as grain silos is a complete, and I mean COMPLETE idiot.