My gut feeling about this that there is no money in flour. It’s not an absolute necessity, as most people don’t use it, buying their cakes and bread already made and it is thus relegated down the pecking order in the supply chain.
I used to notice in my local Waitrose (prior to all of this), that the flours usually remained unstocked for the longest period of time after there was a major shopping period eg. Christmas, Easter, last days before kids returned to school in September. That and the middle size of plastic freezer bags. They would hold stock of two of the three sizes and forego the middle size until there was space on the truck. Kitchen rolls would also often be out of stock too.
My local was anecdotally always the least profitable store in the country, due to supply and floor space constraint and there was talk of it closing. It was relatively small and was apparently difficult to get large trucks to. As a result shortages were fairly common as there was a limited amount of truck capacity. Choices had to be made and those three items would often be the most affected, being either bulky or unprofitable.