What’s wrong with Diana Krall?

@french_fries, yes it's all a question of taste. I'd rather the smooth sound of Ella or Diana rather than the squeal of Billie or the histrionics of Aretha.

That's not to say both Fitzgerald and Krall don't occasionally stray into territories I find bland, but that's my problem.

As for the Beatles, all other bands must look and wonder how..

I am a huge fan of the Beatles, but the Rolling Stones wrote some pretty amazing material. I never gave them the full credit they deserved. 
There were many superb rock groups that also deserve a ton of credit for their contribution so I won't list them. But ALL of them had their "off" days. I can't imagine Mozart not finding the right notes for his latest score, but I'm sure it happened every once in awhile. Not Bach of course...

Yes! I had the same experience. Twice. Once at her performance at the Beacon Theater in NYC a few years ago and recently at a “special “ performance at the Rainbow Room with Tony Bennett. At the Beacon she did everything as you described. At the Rainbow Room she was unapproachable, unlike Tony Bennett who posed for a selfie with me. I paid $1,000 for a VIP ticket and was treated like a poor relation. Something is wrong. In fact that’s how I found your post here. I googled “does Diana Krall hate her fans”.

'Few classical music lovers would think jazz bad taste , many are jazz fans themselves .Most I know think of rock as bad to horrible taste . They don't hate people who love rock, they pity them .' 

I think you're talking about an elderly generation that is dying off and did not grow up with rock. They are disappearing fast at this point. I haven't found it true of those that grew up with rock. I listen to mostly classical but also to jazz and rock.

There are interestingly artists who are more consistent than others in providing what the audiences came to hear. I've never heard of anyone complaining about Elton John or the Stones for example. I heard Joan Sutherland a number of times and she always delivered the goods. I saw Ella at Radio City which turned out to be not much before she had her feet amputated. I lucked out. I got a single 3rd row center to a sold out performance. The Music Hall didn't exist. I might as well have been seeing her in a nightclub. She was very wonderful. I felt privileged and it's a night I'll never forget. A dedicated performer even at the end of her career.

No such as 'good taste or bad taste', its just whether a given type on music fits one's particular palate.