I've looked into this, and it seems pretty much down to the retail vs. commercial packaging and the assorted supply chains. Both the packaging materials themselves, as well as the plant capacity to pack a bunch of 5lb bags of flour vs. giant 50 or 100lb bags a baker would pick up. I'm sure FDA labeling requirements/etc. are likely different as well so it's not quite as simple as "find a few trucks worth of burlap bags".
One thing I've done is found a local restaurant supply store and had a friend with a business tax ID add me to their account (account is setup to actually charge sales tax so it's all good there). At these places, very little is in shortage - plenty of flour to be had of all types they typically stock. The only shortages I've noticed have been in chicken at the moment, and of course PPE. Everything else seems quite well stocked for the time being.
The downside of course is that when you want to buy some chicken thighs, your minimum order qty is 40lbs. But I started a co-op buying group with my friends in the neighborhood and just spend some time splitting things up into usable quantities.
It's come in handy for stuff that is hard to come buy in the grocery stores or costco like chocolate chips. Of course, the minimum qty of those is 25lbs so we had to divy quite a few up! The cost savings are absolutely astronomical on a per-unit basis for most staple items.
I've also noticed at least at my local costco they have started to get "alternative" sources redirected from the commercial supply chain. Such as 50lb bags of rice in plane white nylon bags with a sticker slapped on it. This seems to support the theory that packaging (both material and labor) is the bottleneck for retail staple goods.
Add in all the waste of every 23 year old who has never baked in their life buying 20lbs of flour to go bad in their pantry and things.