Brazil wise, maybe it is a conjunction of factors you mentioned.
Prior to 1985, international rock acts were extremely rare here in Brazil. We used to live in a military dictatorship and I don't think Zappa would be the prototype Rock artist one would invite here then.
But then you probably didn't have willing and competent promoters and, even though there is significant following here now, Zappa is not one of the most popular artists you ever heard about. Most people wouldn't know who he was...
Most likely, it could be a particular reason in his own head. Has he ever played in Mexico, for instance?
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