That would explain why the people on the radio 30 years ago didn't want to give the derivation.

Which radio would that be? Thirty years ago dates to around 1985, and jazz broadcasters like Humphrey Lyttelton were quite at home discussing the origins of the word jazz on radio and television at that time.

Now, if you'd said sixty years ago...

I've always understood, rightly or wrongly, that "jass" - the original version of "jazz" - was indeed a euphemism for sexual intercourse. Nowadays it's a computer scripting language. O tempora! O Mores!