Because it belongs to them, and 90% of the inhabitants are British citizens.
Would be neat if the new bank notes actually showed the Argentinians surrendering enmasse after the Brits kicked their butts....
If for any reason I had to put money on it, I’d bet the thing the other way i.e. that it’s the BRITS who’re going to get booted from the Falklands and that right soon. Sort of a longish story as to why anybody would bet it that way but Argentina joining the BRICS combine in the near term figures into it.