The answer, sadly, is simple, and not something that's easy to fix. Basically, when I sign a contract with a publisher, they acquire certain territorial rights. DAW owns the US distribution rights for Toby and InCryptid. Orbit owns the US and UK distribution rights for Newsflesh. Other publishers own my distribution rights in other regions. The pieces I have sold to the Orbit Short Fiction Program ("Apocalypse Scenario #683" and "Countdown") were sold under a contract which, at present, covers only US territorial rights. Meaning that my publisher can't make those properties available outside the United States. They aren't allowed. And buying the rights for every possible market, in every possible region, would make the work fiscally unsustainable for them.
Part of this is tied to the intrinsic value of a property. Say, for example, that we want to sell the InCryptid books to a UK publisher, for a UK edition. This would make the physical books cheaper for UK customers, since they wouldn't need to pay import costs. This would mean I got paid (foreign rights sales are a good chunk of my income in a given year, since it's a way to keep a book that's already been sold paying my electric bill). But if we tell a UK publisher "oh, and by the way, we sold the ebook rights to that series to someone else," that publisher isn't going to buy the series. There's too much tied up in ebooks right now for that to be fiscally wise of a publisher.
Orbit is working on making the short fiction pieces available outside the US; if you check the Short Fiction landing page, they note the problem exists, and that they're looking for a solution. But the solution is never going to be "sell global ebook rights to the US publisher," because if authors did that, the foreign rights market would collapse. Books would remain import-expensive, non-English readers would lose a lot of diversity, and my cats would get very hungry.
It sucks that it works this way, just like it sucks when I can't get the British or Australian TV shows I want on the right region format immediately. It may change someday. But for right now, this is why things are the way they are.