Supposing that this is, in fact, a new policy, there's a way that it makes sense and is good for most of us (i.e. the plain consumer who is MidwayUSA's primary customer):
Selling to dealers causes supply problems for the small-quantity buyer (i.e. the individual consumer). If supplies are tight, it makes sense to protect your core business (the individual consumer) by preventing dealers from buying everything you have of a given item that you might not get more stock on for quite some time.
This may not be a factor in the decision at all, and it may or may not even be a new policy. The foregoing is simply one way in which this policy could make good sense. I, for one, was very appreciative when a local store took my suggestion (which may have been suggested by others, too; I don't know) to limit quantities of primers anyone could buy to two boxes per day when supplies were tightest. That policy assured that people like me, who only need small amounts of those items, have a stock available to them from the local business. Absent that policy, I'd either have had to stop shooting, or I'd have had to buy a relatively large quantity from a mail-order house, which means I'd not have gone back to the local outfit. It's possible, just possible, that Midway has/had a similar thing in mind.
Personally, I've been distinctly irritated with Midway for a while because of their decision to not only take shipping out of their products' prices, but also to make shipping a secondary profit center. They also did relatively little for me with a barrel I bought from them a few years ago with an improperly-made chamber. Having said that, they recently honored the lifetime warranty on a MidwayUSA-brand tumbler (which they haven't labeled that way for years) by sending me a new one no-charge. I appreciated that. Even though it was merely adhering to the warranty, I kind of expected them to try to dodge that one.
I would happily do more business with Mid-South, but they're just enough further away that their total cost is higher than Midway's (or others), mainly due to shipping. I really wish we had a major supplier in the West.
All that said, in these recent times of shooting-sports manufacturers, distributors, and dealers being able to charge essentially anything they want for most everything they have, it could also be simply a case of wanting to make the most money possible before the crash crushes them and everyone else.