From the time the facility was built and up until the 1980's, I don't think the safety bug had bitten the company. Most of the employees were the typical small-town and rural men who were a tad casual about safety anyway.
(It was quite common for farmers and men at elevators and crop production businesses to be missing fingers, etc... sort of like railroaders a generation earlier.)
My guess is that cleaning the stacks wasn't done that often, was seen as just another part of the job.
Well, I’m no safety paranoid, so for me it would have just been a proper design issue. If some task strikes you as stupid every time you do it, then redesign it so it’s not.