There are several significant differences between KFI's situation and KGO's:
KFI never fell off in terms of ratings as badly as KGO did. They've had a stable morning show (Bill Handel) for 29 1/2 years and a popular afternoon show (John and Ken) for a few months longer, minus two years across the street at KABC more than 20 years ago. And they kept Limbaugh in middays until 2014. When they moved him over to KEIB, most of the audience didn't follow. KFI retained the bulk of it.
Not that nighttime ratings on an AM talk station are ever anything to write home about, but Tim Conway, Jr is coming up on 13 years on KFI.
The tone of the station is remarkably consistent. There's never been a period of "re-invention" even as previous higher-profile hosts (Phil Hendrie, Stephanie Miller) came and went.
They have a small but strong, reliable newsroom with some top-notch reporters.
Probably the biggest problem KGO has? Even if they had come back with unlimited resources and a willingness to spend whatever it took to get to the top, the demo they used to own (well-educated, interested in depth, largely politically progressive) is now KQED's audience. NPR doesn't have that kind of strength in Southern California and the KFI audience isn't the KCRW/KPCC audience.