To begin with, jazz is near the bottom of the list in regard to popularity of music genres; this thread is an example of that, it's at the bottom of the list on "audiogon".
Some have given more reasons than you can shake a stick at for that fact, but the fact remains.
Most of the people you named are well represented and appreciated in "Aficionados collections".
The only way they could be more widely appreciated is to play Rock, Pop, or Rap; but then it wouldn't be jazz.
The people you mentioned are very well known to me, and have been appreciated for most of my life. While we are introducing them to "newbies", they are well represented in our collections, as old aficionados.
The fact that jazz is a very individualistic art, also means that the people who appreciate it are very individualistic as well.
Out of the artists on that list of 6, "Blossom Dearie" is the only one I question. Although I have her in my collection, I wouldn't rush out and buy one of her albums; maybe there is a reason "Blossom Dearie" is under appreciated.
I guess 5 out of 6 according to me, isn't too bad, but Earl Hines is the only one that I could appreciate that I haven't listened to lately; sort of "nostalgic" he is, and today is my day for nostalgia.