Mostly adoption purposes. Bitcoin, for better or worse, is now a globally recognized asset (if not official recognized). Sure they could adopt a coin like Ripple or Doge, but that would almost certainly permanently sabotage the market for both respective coins. While I agree that this is a bad idea, basing it on a larger currency does have some considerable economic benefits.
Not sure why, but bitcoin has already been in use in a local surf town for a couple of years now, so maybe it's the only widely known crypto in El Salvador outside the crypto community [1]
