Thing is they designed the silo as a crew payment / feeding item, with a rediculous extension on the spoil timer.
if other foods would be allowed to be placed inside, it would change from that role into a longterm storage device for all your foods, rendering the other storage solutions obsolete.
They would need to rework all food storage items, changing spoil time increases, who and what they feed, and the fuel needed to power them.
As a quick fix they could make it so that you can only put stuff in the silo and not take them out - this would keep it's use as only a crew pay / feed item.