Yes this is a problem -- and my wife and I have just accepted it and use two separate accounts -- one for Japan and one for the USA. Amazon in Japan is so far superior to the US it's not even funny -- but living in NYC we have it pretty good -- nearly 100% of our orders are delivered by the next morning -- in varying conditions however....

Given the recent exchange rate my wife has been on a spending spree in Tokyo -- I'm glad I'm coming home in a few weeks to end the "but it's 40% off right now" binging in Ginza and Omotesando....

As I've said before, at least for me, you're completely wrong.

My Amazon account works in every country I've every tried logging in, and just yesterday I tried a few more countries for laughs.

Same login, all payments show up, all addresses in every I've shipped to show up. All local offers and discounts.

Amazon will specifically ask me which country I want to use when I make a purchase, even those I've never used before, and offer me a free 30 prime trial if it's a new country. And like I said, I'm not making a foreign purchase from a foreign account, it is 100% native.
I make purchases all the time in the US, Japan, and AUS to those respective countries.

For me there is no difference between having different logins or just using the same account. Under options I can select what my default country is, but it always asks me anyway when I buy something.

I was referring to the issue in prime video -- but thanks for all the other stuff.... And just so you know -- it's not limited to just certain countries -- I don't know why it happens but it was frustrating enough that we just gave up and maintained separate accounts.... We also use Amazon Music, I use Amazon to watch NFL football, and there are many other "bugs" they have. Personally I think it could be licensing issues, but as someone that lives in both places having two accounts just made life easier...

I'm currently in the UK -- here is what Amazon tells me (and I've found it to be true) when trying to use Amazon outside of my "home" country:

Oh, sorry, ACK.

Probably the same bug with your NFL subscription.

I've never had an issue if I just change my home country on prime video in the options setting to access the regular local content, non special subscription. Music works fine for me.

I've found the apps on different devices are wildly different.

I carry a Google TV with Chromecast wherever I go and enjoy whatever countries content I want, so doesn't seem to agree with the answer Amazon gives.

Very helpful since licencing differs between different countries, some content is only on Disney+ or others in different countries, but Amazon will licence it in the another country.

Of course I use a VPN to access the country I want. That's probably what breaks it.

I probably should have been more selective in my quote ;) -- My wife is Japanese and although we can make things work with one account we've run into so many issues that yes -- can be resolved -- but require so much work it's not worth it.... Amazon Video was just one example - Netflix also gives us fits - as does NFL football (my kryptonite). Yes - buying stuff is simple -- but all of the add on services we've added somehow make things complex....

I probably should have been more selective in my quote ;) -- My wife is Japanese and although we can make things work with one account we've run into so many issues that yes -- can be resolved -- but require so much work it's not worth it.... Amazon Video was just one example - Netflix also gives us fits - as does NFL football (my kryptonite). Yes - buying stuff is simple -- but all of the add on services we've added somehow make things complex....

Almost certainly country licencing. I have had Prime Video, Netflix, Disney+, Paramount+, work in every country as long I use a VPN and set the home country in the app's options.

Easy as, just click the country you want to be local in and it just works, and each offers a completely different set of content to the others, mostly cross mixed across services.

Some, like Amazon, you need to add a prime prescription for the country you want, most others have a universal subscription that automatically gives local content.

But all work with the same login as long a I remember to pay for the country I'm interested in.