Is it a case of "can't compete" or about cost of importing to the USA and traditionally the USA seemed to want very cheap budget scopes, having spent a lot of time out there it seems that was the case, even my relatives in Canada don't spend half as much as we seem to on kit and optics.
No experience with Z5 but the Z6 range are superb and somewhere Youtube? a poster visited Swaro factory and some revealing stuff worth a look, also Z6 & Z8 always been rumoured same quality glass and my findings were that and went for Z6 as use to a big saving over the Z8 range yes there might be benefits but were not enough for the big price difference.
Lots of choice's and have a proper look through them all as everyones eyes are different my eyes work with Swaro and not so well with Zeiss or S&B.