if it’s as easy as having your bank send money to someone else’s bank, why does western union and transferwise exist?

[Transfer]Wise is typically cheaper than bank to bank, they (the banks) charge relatively heavily (at least for normal retail current accounts) for IBAN/BIC/et al. transfers.

But yes it is possible, and as easy as entering some different/extra numbers compared to intranational sort code/account number transfers.

That relies on banks in the sending country participating too, or El Salvador opening it's own banks in those countries doesn't it? How do they get sending banks to participate in these cheap/free international transfers?

Sorry, that was perhaps unclear, that 'they' referred to the banks, in the case of bank-bank.

Bank-bank requires that the bank at both ends supports sending/receiving to/from (as applicable) IBAN or similar yes. In the UK in practice that means 'mainstream' banks do and 'challenger' banks don't. (Monzo for example prefers to solve the problem by integrating Wise a bit into its own app.)

Wise avoids it by charging you (like paying for any other product/service) or having you transfer to its account in your country, and then sending the payment to the destination bank from its account in the same country as that, so it becomes two local transfers, one in each country.

Because if you're not in the country legally you don't have a bank account.

If you can just do that then why does WU exist?

Is this the thread where US Bitcoin fans learn that the rest of the world has been doing this for decades?

I'm being sarcastic. Bitcoin in an amazing solution that allows people working in the west to send money home direct and takes this trash company out of the equation.

So basically your solution is to give everyone in El Salvador a bank account and for the government to subsidize their remittance fees. Because if you're using banks, someone is paying fees. Someone from the US still has pay a fee to wire money from their bank to some endpoint in El Salvador.

The banks are literally the problem that Bitcoin solves, not the solution. Banks = fees and censorship.