Executive producers Michael Filerman and creator Earl Hamner made the wise decision to make Robert McCullough the supervising producer and de facto show-runner by the end of the first season, and the result was three years of FALCON CREST which were near-brilliant -- a gently Gothic, slightly tongue-in-cheek entry in the DALLAS/DYNASTY era wealth-based nighttime soap genre which became so huge during the early-1980s.
Unfortunately, studio politics at Lorimar Productions resulted in a lunch-drinking executive demanding that McCullough be fired, even though the series was at its ratings peak, and FALCON CREST was never, ever the same again. Ever.
Once McCullough was gone, the show managed to maintain some momentum for a few months through most of its fourth season, but a CBS executive then demanded that the "offensive" nazi treasure plot line be dropped immediately, just ten episodes before the end of the season -- despite the fact that it was the year's main storyline. As a result, the remainder of the fourth seasons sees a bunch of side plots cobbled together and shoe-horned in just so they can finish off the year. But to me, the inertia of the program had been destroyed once and for all (even though its cushy post-DALLAS time slot kept it alive for several more years).
Season 5 was drab and cluttered. Season 6 seemed like it might be a renaissance for the show, but it turned too much towards excessive shlock by the end of that year and then Season 7 just became frenetically silly. The decision to turn the production design light and airy and '80s pastel, combined with Lorimar's new cheapy post-production process making the show look as if it had been shot on video, didn't help much either. A big ratings drop during Season 7 saw CBS demanding the show be fixed, but once they tried to get serious again for Season 8, they no longer seemed to know how to do it. And by Season 9, it just seemed like a different series entirely and ratings continued to spiral into the cellar.
Why do swollen executives think a show can make itself as long as you have a key star and a recognizable brand name title? Because it can't.
Shame, because the first three season, maybe even 3 1/2 seasons, were fabulous.