Cause they suck. I grew Joey, yech. Big seed, small fruit, grassy taste. Waldin (pure W. Indies) or at least one of the Florida "Slimcado" pits would be a good rootstock as they can take saline water really well. Starting in 2012 I grafted to those pits because of my hard well water which has a TTS up to 800ppm! Not only was the rootstock very vigorous, was ready in 2 months but all the grafts took.
Whatever, you can't fight mother nature. Plant only what will work for you.
Joey:
Other choices would be the very high quality, rich, slow growing SoCal "compacts" like Pinkerton, Gwen or GEM. Put them in RootMaker pots and shelter them when temps dip below 30F. I grew Gwen until a heater failure. It stayed a runt for the 4 years I had it. My Pinkerton and GEM are very slow growing. They've taken the greenhouse heat really well too. Also low RH.
Good luck!