> El Salvador switched from wire transfers to BTC because the president wanted to.

The country switched to using BTC as legal tender because it was already being used as local currency because the people were using it for payments due to the lower fees.

> That person is usually going to charge more commission than Western Union for the privilege of doing so, because they can.

It seems like you're assuming this to be the case without having any real knowledge of the situation. BTC was adopted by El Salvadorans exactly because they were able to spend less on fees over the competition.