Is the reason for that actually technical, or is it that U.S. numbers/datasets are the most attractive targets for scams (i.e. due to the supply of victims, access/availability of data, ease of not having to worry about i18n/l10n for your scam tactics, etc.)?
also the extreme number and variety of number of weird small CLECs, foreign SS7/PSTN operators, and grey market voip operators that interface into the US phone system vs a much smaller market like the UK or Denmark or somewhere.
