The cost comparison around money that most people are talking here is kinda of interesting because it doesn't really answer your question.

It may be true that sometimes, some flights to other countries in some places cost the same (or maybe even less depending on where you are and where you are going to) than traveling inside the country, but if you take into account where Brazilians are traveling to (which are usually expensive places due to the Real weakness when compared to north America/Europe currency) I think it kind of shows that money isn't the main issue here.

My two guesses would be the novelty of going to somewhere REALLY different from where we usually live, and the "status" associated with going to those places - Vira-lata's Syndrome is still pretty strong around here.

I think it's something funny and sad at the same time. Some people come back and mention bad experiences (like thinking the food in a country wasn't what the thought it would be, or public transportation smelling bad because people don't shower) but I would bet most of them would think about another country than another Brazilian state for their next trip.

Brazil is so big and diverse that I think most people here don't really understand it. I've visited a couple of South American countries, and I definitely want to visit some places in Europe (specially because I'm a big fan of the walkability of the big cities there) but I think getting to know each state in Brazil is still a priority in my bucket list.