Because Rick Dees didn't represent Los Angeles, he represented himself. Just was reading about his 10 Million dollar law suit which he paid along with ex KIIS GM Wally Clark for skimming profits on his Weekly Top 40. Rick was not known for his goodness, even lost his million dollar Liz Fulton lawsuit, partly because of this evidence (watch at the 7 minute mark), and the way he treated people in general.
https://www.youtube.com/watch?v=H9A7EdC3sGw
Rick Dees had a great career and was definitely a huge radio talent and any list of great LA Radio personalities that doesn't have him on it is wanting. That said, there are definitely some attributes that I believe has lessened his status over the years. The biggest one is that when Rick was (unceremoniously, for sure) told his time on KIIS was over and it was time to pass the baton to a talent of a younger generation (Ryan Seacrest), he didn't handle the situation with very much grace. Instead he seemed to publicly pout about it in a very passive/aggressive way, looking for another station that was aimed at the younger demographic to just immediately pick him up, which of course didn't happen (validating KIIS' decision in the first place). The hit music format had indeed passed him by, even if he didn't want to admit it.
The rumor at the time was that KRTH wanted him bad for their morning show and was willing to write the check to make it happen. This would have been a natural move for Rick as people in my generation who grew up listening to him in the 70's and 80's were already mostly transitioned from KIIS to KRTH anyway. If he would have moved into that chair then, there is a very good chance he might still be there now, and people would talk about his longevity just as they do for others that have been mentioned on this thread. And it's not like it hadn't been done before - Dick Clark went from broadcasting to teenagers to being the imaging voice and TV commercial personality for KOST for years, and that was back when KOST was still playing Barbara Streisand and Neil Diamond records.
But the real issue is that once all of that had passed and he was eventually given gigs at Movin' and later Hot 92.3, the show simply wasn't the same. I don't know if he was just too busy with his other pursuits, or just plain lazy, but it was clear that he was not putting in the same effort to make a quality show. I said at the time that I thought he was just phoning it in. I think a lot of others must have thought so too because his audience didn't really follow him to those two stations.
By choosing not to grow old with his audience, he sacrificed them to continue to try and be young and hip to a new generation's audience that in turn only saw him as an aging DJ to which they did not relate. In the end, he lost both audiences. I believe this is why he doesn't get the level of respect his otherwise excellent career warrants.