Because it's not so easy to add new currencies. There can be all kinds of barriers, from accounting complications to lack of support from payment processors.

Are you referring to the currencies available to PayPal or Stripe for direct payments, or adding a special payment provider for BRL?

Adding a new payment provider has a lot of logistics involved (I think I talked about these in another thread with you). We have to be careful about what new providers we add to ensure we can have the same set of features and don't overload ourselves with overhead.