It seems so bizarre that so much flour is being consumed now. Are people hoarding it, or would this demand otherwise have been met from restaurants?
Think about how often people bake normally. Not often. Now it's all the time.
Same reason why eggs and vanilla are also harder to find in some places.
Store pickup also complicated things as you usually only get about 60 to 70 percent of the items you ask for, and usually it's the sundries that get knocked out. So you can ask for all the ingredients for a complete meal plan and wind up with all the vegetables and a little meat but nothing else. Or you get shorted on other aspects of the pickup(this is just a bare statement of fact). We gave up and just went into the store with homemade PPE.
I do think this situation is revealing just how fragile our system of just-in-time delivery and globalization is. For things like N95 masks national borders are very real, and being dependent on China for everything in the US is really really bad.
It's also highlighting for me how important it is to know how to cook and be fluent in different kinds of cooking besides the standard American diet. When this first started the store shelves were picked clean of anything that most people recognize as nonperishable food. So I grabbed things like textured vegetable protein and millet. The shortages are really only a problem if you don't cook from first principles or don't have much experience with spices or other sources of flavor.
Making a grocery store run about once a week (earlyish AM on a weekday) is one of the few compromises I've been making to just staying on my own property or adjacent basically unused forest trails. And the reason is as you say. I find a lot of real-time adjustments are still needed depending upon what's in stock.
ie. if people are baking more and buying bread less.
Now, my bread purchases have gone to zero (Since we go shopping every few weeks, and have no room, or interest in freezing bread.) I'm not eating out.
My net consumption of flour probably hasn't changed much, but my purchases of flour have gone up, dramatically.
It's probably all logistics and supply chain issues because everything was geared towards delivering 1000lb loads of flour to a bakery instead of 100 x 10 lbs bags of flour to the grocery store.