Would it be better if the extortion were in Euros or Yen?
Who would be so stupid to try and extort people using those currencies?
Extortion predates Bitcoin
Well to start with, the Italian mafia and the Yakuza, respectively.
You missed the currency joke.
No, because it would be a lot more traceable. Why do you think cryptolocker and its variants are suddenly popular. Bitcoin's relative anonymity allows it.