The reason why US Dollar is prone to counterfeit is because of the core material (linen & cotton) there bills are printed from, while that barely happens to countries (like the UK, Australia, Barbados) who print their currencies using polymer with transparent windows or panels.

I mean, there have been attempts of people counterfeiting polymer currencies but to no success as it’s obvious (mistakes are guaranteed to be detected, it’s hard to “fake” a transparent window) since polymer bills have a different texture and have braille in comparison to US Dollars.