That ended about 40 years ago. The advent of phase lock loop FM radios (especially in cars) made a huge difference.
In 1978, seven of the top ten stations in San Francisco were AM.
1. KFRC-AM (Top 40): 8.4
2. KGO-AM (Talk): 7.6
3. KSFO-AM (A/C): 6.5
4. KCBS-AM (News): 5.8
5. KFOG-FM (Beautiful): 4.4
6. KIOI-FM (A/C): 3.9
7. KABL-AM (Beautiful): 3.5
8. KSFX-FM (Disco): 3.4
9. KNBR-AM (A/C): 3.3
10. KDIA-AM (R&B): 3.2
By 1985, it was four of the top ten.
1. KGO-AM (Talk): 8.8
2. KCBS-AM (News): 5.3
3. KYUU-FM (some called it A/C, some called it CHR): 4.1
4. KIOI-FM (same as KYUU---if these were A/C, they were very hot A/Cs): 3.5
5. KSOL-FM (R&B): 3.4
6. KABL-FM (Beautiful): 3.3
7. KSAN-FM (Country): 3.2
8. KFRC-AM (CHR): 3.1
9. KNBR-AM (A/C): 2.8
10. KFOG-FM (AOR): 2.7
10. KRQR-FM (AOR): 2.7
Of those, KFRC-AM fell below a 1 share in the mid-90s (it was simulcast on 99.7, which did quite well), and by 2005 was expendable when CBS needed to dump a Northern California signal to buy KOVR-TV in Sacramento, KCBS began simulcasting on FM in 2008 and KNBR in 2019. Because they use single-line reporting, we don't know what percentage of those two station's audiences are still listening to the AM, but the belief is that it's well below half.