You don't, as a rich person, want to have all your assets in a single jurisdiction. You want to spread them as far as possible, for multiple reasons, and for this you need a cheap transfer way:
- resilience against political "changes" (esp. China, Russia); money that is under foreign, unaffiliated regulatory regime cannot be seized by authorities at home
- taxes: you want to secure your cash/assets from sudden taxes on property/equity
- resilience against a bank going literally bankrupt. this happened in the financial crisis, even in the EU, and one bank's customers IIRC lost everything above 100.000 € on their accounts.
Also, if you run an international business with regional offices or such, you don't want to spend huge amounts of both time and money when transferring company funds or buying machinery from vendors in other jurisdictions.