It's important to note that El Salvador's currency is the US dollar. WU doesn't even need to convert currency. They are simply taking up to 10% from a low-earning demographic group in the US just because they can. Even if bitcoinization itself "fails", if it forces WU to lower its fees it'll do net good.

Among U.S. Hispanics and Salvadorans, the median annual personal earnings for those ages 16 and older was $25,000.

Salvadoran Americans, even those who are poor, have an incentive to send money to family and friends in El Salvador because a U.S. dollar buys much more there than in the States. In all, they send approximately $800 million back home per year—close to $1000 per person

1000 bucks per person is not some exorbitant amount, it's some people's yearly starbucks budget.

https://www.everyculture.com/multi/Pa-Sp/Salvadoran-American....

https://www.pewresearch.org/hispanic/fact-sheet/u-s-hispanic...