I opted for es-419 over es-ar for kinda the same reasons I opted for zh-yue over zh-hk for Cantonese. Languages don't stop at political borders (some moreso than others), and if there's a code that reflects that, I'll use it.
But yeah, it's odd, but apparently it's a real code. And at least according to the Internet, it's possible to do "neutral" non-country-specific American Spanish, and that's what I want for these if possible. They might not be there yet ;)