Those are all Vanguard funds. Specifically the ones that hold entirely non USA assets.

Personally, I prefer Vanguard over other US brokerages, say Fidelity, Etrade, Schwab, etc because the company itself is owned by the funds you purchase, rather than outside investors. As weak a reason as that is.

i've previously read that many non-us banks and some brokerages don't like (read:may refuse) doing business with americans because the USA has strict tax rules and need for disclosures (I think if the cumulative total of all a citizens foreign accounts is over $10,000 it must be reported). If you have recomendations for foreign brokerage accounts, i'd be interested to know more.

The vast majority of americans do not have significant disposable income, and will be primarily investing in their 401k (employer match for a certain %, as well as tax advantage), if at all. Typically employees are locked into whatever brokerage their employer opts into. Without a 401K, they might instead be using an IRA for tax advantage, but I doubt there are many foreign financial institutions that would/could offer a US IRA.

That may mean that convincing your American friends to move accounts could be difficult (or impossible) vs just having them invest more into foreign funds at their US brokerage(vxus, etc).