Generally speaking , as far as I can tell, opera is sung as far as possible without a particular class or regional accent. Each language has a well understood sung form that isn’t exactly like RP speech but is clearly close to it. I know that there are a few Italian works where a comprimario role takes a Sicilian accent and Baron Ochs in Rosenkavalier is supposed to be comically rural but these are minor exceptions for effect. Why then the tendency for modern works in English to require exaggerated accents? And why is it so uneven? Nobody expects the characters in Peter Grimes or Albert Herring to sing with Suffolk accents but apparently Anna Nicole requires singers to do a really bad fake Texas accent and A Streetcar Named Desire seems to be thought to require a similar treatment.
Does the same thing happen with modern operas in other languages and does anybody have any explanation for why it’s suddenly crept into the English language repertoire? The only explanation I can offer for Anna Nicole is that it’s part of a whole cultural appropriation/condescension thing that is going on in that work that I find quite intolerable.