Could definitely be varying regional demand, but dealers near me don’t have any sitting besides their demo. How are you checking that dealers have one sitting for weeks and months?
The car search sites are not accurate. For example my local dealer has 10 (!!) Lightnings listed on cars.com but zero on their own website. I drive by it twice a day and they don’t have any sitting. Not sure what’s going on there. Maybe they have some system that lists everything earmarked for their dealer automatically on cars.com, but those may already be all spoken for.
Ford also requires dealers to keep their demo/mannequin for something like 6 months or 6000 miles before they can sell it or else risk fines or reduced allocations. So yes there could be a lightning sitting at each local dealer for months.
A lot of dealers have their demo listed as “in stock” for sale but don’t tell you it’s a demo that can’t be sold until you contact them.