What prevents an end user to either buy a japanese vpn and use that to connect to the app store.

I doubt that a vpn running itself inside an ios phone itself would work out of the box but what about if its running at a router level or lets say I use a vpn on another phone and use it to create a hotspot to connect to in an ios phone.

Don't things like these basically allow these rules to effectively break the ios monopoly.

Or think about it this way, lets say I go to japan and install an third party app store and then go back to some other country, would the 3rd party app store still work?

I am also wondering about what mechanism can be used which can make a third party store work in the first place, I know of IOS jailbreaks so would it be similar to it, how would they detect that its in "japan"

Or would these work at a hardware level? That a phone sold in japan would have such features, if that would be the case, I would assume it would increase the values of such phones.

I would appreciate it if people could tell me more about what's the case and answer my questions.