(Fresno, Long Beach and San Diego no longer have their ECHL teams. The last really needs a new arena, but the existing ones previously hosting ECHL franchises in the first two cities, could be suitable for an AHL team.)
If you're going to say that San Diego "really needs a new arena", then you have to say exactly the same thing for Long Beach. While that team did last one more season than the ECHL San Diego team, the arena is much worse -- too big for the ECHL, too small for anything major league, and the hockey sightlines are fairly horrid, especially from areas in the lower bowl (the bowl is circular, not oval, thus the upper bowl is tremendously far away from the ice at the sides). It may be "newer" than Selland Arena in Fresno (and larger), but Selland works well for hockey -- the Long Beach Arena never was a _good_ fit for hockey, which is unfortunate, given that the die-hard fans there were some of the best "road" fans I ever met when I was visiting arenas other than my home arena.
Plus, if you figure in the historical attendances of the two markets, comparing IHL attendance to IHL attendance and WCHL/ECHL attendance to WCHL/ECHL attendance, then San Diego is a much more attractive AHL market than Long Beach, IMO. Add into the equation that the existing (45-year old) arena in San Diego has its lease owned by none other than an AEG company, and you have it being much easier for the Kings to move an AHL franchise into the facility than it would be for any of the other theorized AHL franchises to move into Long Beach and/or Fresno.
Of course, I'm biased here, as a 16-year San Diego resident, and I admit that. But even putting that bias aside, you can't seriously say that San Diego "needs" an arena before they get an AHL team and let Fresno and Long Beach slide on that front.