This action shows how much El Salvador cares about Bitcoin adoption to reach really high levels. After making Bitcoin legal tender, they are trying every way they can to convince their people to start using Bitcoin as their main currency. And this is a clever way of doing it. If they place these Bitcoin ATMs to the right places like gas stations etc., they can benefit from it a lot.
This country allows legal Bitcoin bidding, so they don't need to set up Bitcoin ATMs but force people to accept Bitcoin for payment.
I can't see a bigger benefit than the ATM's Bitcoin advertising. It may be a waste of money in the short term, but it has long-term effects on El Salvador's Bitcoin payment policy.