Boo, face it, very few people want to hear real jazz, at least more than a song or two. On the other hand millions love to hear three-chord blues shuffle songs. Sure it was out of place at a true jazz festival, but the term jazz is tossed around pretty loosely these days, and the audience was just revealing that they liked what they heard, regardless of whether Boo likes it! smile
Even New Orleans Jazz, as you know, isn't the same as other types of jazz. I've heard so-called jazz bands play nothing but Big Band stuff from the 40's all night. Check this list of "jazz standards". Everything from blues, folk, pop, show songs, etc., on it.
https://en.wikipedia.org/wiki/List_of_jazz_standards
If jazz doesn't evolve then the remaining fans will all die off and there will be nobody to listen. Are there any jazz songs that aren't 50 years old? Wasn't All The Things You Are written in early 50's? Nothing wrong with old songs; I love 'em, but if you want to interest young people in jazz, then jazz has to evolve. Country music has evolved so that younger people are into it, even though I hate most of it.
R.I.P. jazz as Boo knows it! frown
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DonM