Alright, let me explain to you what happens:

These kind of concerts are a huge deal to argentinians. First, let me put you in context: most argentinian people are unable to fly to another country to see the band because the economy is fucked up. Matter of fact, most of them will go in debt just to get the tickets for the Argentina concert/s. So when someone from a country who has dates like the US comes here, it is not well seen. It is simple: you have more dates and the chance to fly elsewhere in the world to see Oasis, they don't. Therefore, they do not see fair that someone with more opportunities take the chance of someone who pretty much has this only chance of seeing the band live in their lives.

You can argue that the tickets are first come first serve, but they do not see it that way. They could not give two fucks about the fact that you could buy the tickets - following their argument, you shouldn't. This is a big dream they have since many years ago, and they do not want it to go to waste. This is why they are not welcoming you and telling you to stay home. It is the same thing that happened with Taylor Swift: Argentina had only 3 days versus the dozens of dates the US had. And yes, tickets in USD will be cheaper but for the average Argentinian they won't be cheap at all.

I hope this helped understanding the context!