If you want an EU styled vivarium in the USA you can get one from custom builders which is why there is no market to ship from from Europe, and obviously they are not that popular in Europe because no one has made a major company out of it just like the USA.
I'm Canadian so our market is a lot smaller. It looks like it's still relatively niche in the US but you have more people = more custom options.
I'm not sure how popular or not they are in Europe, maybe @Tijil or someone else can chime in, but I do see a few smaller companies with what looks like high quality product.
Exo terras actually are from Europe if my memory is right. I do not consider Eurostyle vivariums to be a better design, its had its fad time in North America and it passed. If it was so great it would have stuck but it didnt. The design has multiple issues.
First I've heard of this take on the design. I've never used one, so I can't speak to the efficacy of the tilted floor; I suspect the way I tend to design and run tanks it wouldn't be much of an issue for me. The one place I feel Exo-Terras are superior is the swing-out doors; I really like them and there's no track to be concerned with cleaning etc.
Also in the many years I have been dart frogging I have seen a number of vendors pop up to make custom sliding glass vivariums of different styles. Sooner or later they all seem to give up. I think the problem is the profit just isnt there to keep them going.
No argument there, but I always thought it was because custom built enclosures like that are inevitably expensive and at least here in Canada, I've seen a lot of hobbyists are either acutely budget conscious and/or would rather spend the funds on accumulating more species. That's not a judgement one way or the other, the frogs don't care if they're living in something expensive so long as their needs are met, it's just what I've seen both with frogs and reptiles in general over 20 or 30 years in and out of the hobby.
[...snip...] and I would gladly sell out my entire country and become a vassal state of america just to get ahold of Lepidobatrachus llanensis from the frog ranch in the USA.
That's ... veeerrry specific.
Canadians are envious of the somewhat easier accessibility of large Oophaga species in Europe and the US. Given the expense and risk in shipping long distances, and the need to create a large founder colony to ensure the sex ratio, it's prohibitively expensive to get that started here. Not impossible, they're around here and there, but we're years behind on that front.
[...snip...]
Myself, like most others I imagine, had to settle for an exo-terra and modify it for my purposes.
[...snip...]
And with more people staying and working at home, this hobby is only going to get more and more popular, furthering the demand of such a product.
My only major gripe with Exo Terras are the lids and the lack of larger options. As for the popularity of this hobby, I have no idea. Herpetoculture in general is bigger than ever, but I don't know about frogs, especially here in North America.