Since Hodgdon doesn't make any of the powders they sell, they're pretty much at the mercy of the companies who actually make the powders. They can specify what they want a powder to do, or the kind of powder they want (flake, ball, cylindrical, flattened ball, etc.), but they have to find a company that either has the equipment to make the powder they want, or has the extra capacity to add another powder into their product line. Or is even willing to take on another product...
In the case of SR4756 and SR7625, the manufacturer no longer wanted to make those powders, and they weren't top sellers in the whole scheme of things, so Hodgdon was no longer able to get the product. Powder is truly a product of the global economy, so Hodgdon has to get their products where they can. It was a smart move to get General Dynamics, Canada to agree to make the Clays line of powders, instead of depending on ADI in Australia, with the association shipping restrictions for transoceanic shipping of gunpowders. Now the product can be shipped in trucks, one right after another, instead of waiting for their "ship to come in", so to speak.
I've talked to Chris Hodgdon at the SHOT Show and he's a really nice guy, as is CB Hodgdon, though CB is pretty much retired from the business now. We talked at length about finding a replacement for 800X that would actually flow through a powder measure, and Chris and I both tried it in our Belding & Mull measures. We agreed that if it won't meter in a B&M measure, it isn't going to meter through any measure. He uses 800X for some of his loading and cusses it just like I do. He said they couldn't find a powder company that could produce the same burning characteristics as 800X in any other configuration. In a way, they are just as much victim to the manufacturers as we are, and in some cases, victims of the technology, or lack of it.
I'm just glad they're as consumer friendly as they are. When you talk to them in person, you can feel the frustration level, which is the same as ours. They'd love to sell the product, if they could get it, and they're working on it. It just takes time to get the process worked out.
In the case of Winchester 231, the problem is supply and demand. A lot of the ammunition manufacturers use 231 for their handgun ammunition, so the demand for that particular powder is extremely high from the big boys. Money talks, and when you have guaranteed sales that you depend on from year to year, you, as the manufacturer, are going to take care of those steady customers, since that's income you can depend on for the day to day operations. It just makes good business sense to channel the product that way, and since there is still only a finite production capacity, we're stuck with the situation for awhile.
Hope this helps.
Fred