Because they have fixed costs to enter the Argentine market. Getting IP protection, getting deals with distribution, and all that while also having a smaller audience than the US means fixed costs that aren't so obvious will be greater expressed per ticket.
I guess there are copyright fees, rental costs, local taxes, etc.
Anyhow, all I read are rants and hardly any comment on the issue itself (anyone wants the tickets? price was not open to debate) or the quality of the show or constructive educated comments on the opera.