I agree. When the feature launched last year, I asked Netflix about this specifically and was told it was about whatever studio agreements they could get. And even then, some Netflix Original content (Marvel), isn’t always available to download. From what I was told, the goal was certainly to get all future content as downloadable, but the politics behind that aren’t going to work with every studio.
Amazon has a more-limited library, but it was able to get download support (at least on mobile), early on as part of its contracts.
The problem with regions is an even bigger can of worms. Although Netflix is doing a better job trying to solidify its library across regions, it has to make separate licensing deals in every single markets in which it operartes. The licensing side of entertainment, especially internationally, hasn’t modernized the way you would think it has, and the companies or groups who own a license in one place often don’t own it in another. So sales teams have to negotiate every single title, often separately, in every single region. One of the reasons Netflix has prioritized its own original content is that it can guarantee it is licensed in all of its markets. But even then, in the early Netflix international days, there were a few instances where flagship Netflix original content wasn’t available in some markets because that content was actually co-financed by studios that sold the streaming/VOD/rental rights to other traditional networks or local streaming services. That was quickly resolved, but it just showcases how hard international licensing can be for content playback, let alone licensing for download. This is also one of the main reasons Netflix had to aggressively target VPN users who would access the larger content catalogs in other markets. In order to get more robust licensing (as well as to actually enter certain international markets), Netflix had to prove it was actively enforcing geo limits.
It sucks and I’m not defending it, just providing some of the business context.
Amazon is so limited in its international expansion with Prime Video that it hasn’t had to address most of these issues. As Prime inevitably expands, it will also face these same challenges. (Hulu, too. Though Hulu has made some international attempts, largely through partnerships with existing local services. Hulu’s dilemma is exacerbated by the fact that it is almost wholly owned by the major American broadcast networks, who already have their own robust international licensing and sales divisions that aren’t keen on being disrupted.)