Just curious
It's interesting because CBS bought KNX-AM in the 1930s, and didn't add KCBS-AM until 1949.
Because the FCC allows it.
Seriously, for many years, call letters for radio and TV had to be co-located in the same city. Because KCBS had been in SF for a long time (it was originally KQW), CBS had to use KNXT in LA, which was related to KNX radio. Why they didn't use KNX-TV, I have no idea.
There are a couple of pieces to the answer.
Until after WWII, the networks didn't seem to have any interest in branding their biggest O&Os with network-related callsigns. CBS in New York was "WABC" on radio (from the old Atlantic Broadcasting Company) and "WCBW" on TV, NBC Red was "WEAF" on radio and "WNBT" on TV, and NBC Blue was "WJZ" until the network became ABC after splitting off from NBC in 1943. That was the point where it started to be weird for the CBS flagship station to be "WABC," and is likely the reason CBS decided in 1946 to buy the "WCBS" calls from the station in Springfield, Illinois that had been using them. (The WABC calls finally went to the former WJZ in 1953 after they'd been dormant for a few years.) And once CBS got "WCBS," NBC was compelled to get "WNBC" for WEAF - they coordinated it so both stations took their new calls on the same day in 1946, IIRC.
The West Coast came a little later, and again it was one network pushing the other to make a similar move. San Francisco was indeed the business and production center back then, and so it was the San Francisco stations that served as the network flagships. NBC turned "KPO" into "KNBC," and CBS turned "KQW" into "KCBS," both in 1949. ABC was less established in San Francisco, and its connection to Paramount in the 1950s made LA more of a West Coast headquarters for ABC, so by the time it got the "KABC" calls away from San Antonio, it put them on KECA radio and TV in Los Angeles instead of KGO radio/TV in San Francisco.
It wasn't until the 1960s that NBC changed its TV O&O callsigns to align with radio - WNBQ in Chicago became WMAQ-TV, for instance - and when KNBH in Hollywood/LA changed calls, NBC put KNBC(TV) there and changed KNBC-AM/FM in San Francisco to KNBR-AM/FM. The FCC rules of the day didn't allow calls to be shared in different markets.
I believe Los Angeles was actually the first place the new rule was used in 1983, when KNXT became KCBS-TV, leaving KCBS(AM) intact in San Francisco. As has been noted above, the KCBS and KNX radio brandings were so well established by then that it wouldn't have made sense to change them.
Bottom line: it just sort of all happened this way, based on what the rules were at various times and what each network did and didn't own in each market. If CBS had owned a TV station in San Francisco in 1949, it would have become KCBS-TV and would probably still have those calls today. But Westinghouse owned the CBS TV affiliate, KPIX. Same with NBC, which didn't own its San Francisco TV station, KRON-TV. And if LA had grown up sooner than it did, the KCBS and KNBC calls might not have ever been in San Francisco at all.
San Francisco was indeed the business and production center back then, and so it was the San Francisco stations that served as the network flagships.
In fact until 1930, San Francisco was more populous than LA.
A footnote: The City and County of San Francisco occupy the exact same land area but because they are at the northernmost end of a peninsula they have no room to expand, as did El A. The only way for S.F. to grow is up which, given their earthquake history, does not thrill a lot of newcomers.
Today, San Francisco isn't even the largest city (by population) in the Bay Area (San Jose is larger)
Thanks, Scott - a perfect synopsis, and you clearly have much more knowledge than I. But I believe Channel 4 in LA did not go directly from KNBH to KNBC, but was KRCA, prior to the switch to KNBC - as in the Radio Corporation of American - RCA - which owned NBC at that time, much as GE did later.
And just for a silly historical footnote: https://www.youtube.com/watch?v=qtnsHJCex3s
There are a couple of pieces to the answer.
Until after WWII, the networks didn't seem to have any interest in branding their biggest O&Os with network-related callsigns. CBS in New York was "WABC" on radio (from the old Atlantic Broadcasting Company) and "WCBW" on TV, NBC Red was "WEAF" on radio and "WNBT" on TV, and NBC Blue was "WJZ" until the network became ABC after splitting off from NBC in 1943. That was the point where it started to be weird for the CBS flagship station to be "WABC," and is likely the reason CBS decided in 1946 to buy the "WCBS" calls from the station in Springfield, Illinois that had been using them. (The WABC calls finally went to the former WJZ in 1953 after they'd been dormant for a few years.) And once CBS got "WCBS," NBC was compelled to get "WNBC" for WEAF - they coordinated it so both stations took their new calls on the same day in 1946, IIRC.
The West Coast came a little later, and again it was one network pushing the other to make a similar move. San Francisco was indeed the business and production center back then, and so it was the San Francisco stations that served as the network flagships. NBC turned "KPO" into "KNBC," and CBS turned "KQW" into "KCBS," both in 1949. ABC was less established in San Francisco, and its connection to Paramount in the 1950s made LA more of a West Coast headquarters for ABC, so by the time it got the "KABC" calls away from San Antonio, it put them on KECA radio and TV in Los Angeles instead of KGO radio/TV in San Francisco.
It wasn't until the 1960s that NBC changed its TV O&O callsigns to align with radio - WNBQ in Chicago became WMAQ-TV, for instance - and when KNBH in Hollywood/LA changed calls, NBC put KNBC(TV) there and changed KNBC-AM/FM in San Francisco to KNBR-AM/FM. The FCC rules of the day didn't allow calls to be shared in different markets.
I believe Los Angeles was actually the first place the new rule was used in 1983, when KNXT became KCBS-TV, leaving KCBS(AM) intact in San Francisco. As has been noted above, the KCBS and KNX radio brandings were so well established by then that it wouldn't have made sense to change them.
Bottom line: it just sort of all happened this way, based on what the rules were at various times and what each network did and didn't own in each market. If CBS had owned a TV station in San Francisco in 1949, it would have become KCBS-TV and would probably still have those calls today. But Westinghouse owned the CBS TV affiliate, KPIX. Same with NBC, which didn't own its San Francisco TV station, KRON-TV. And if LA had grown up sooner than it did, the KCBS and KNBC calls might not have ever been in San Francisco at all.
Also worth noting: Channel 30 of New Britain, CT was WNBC-TV before New York City was. You can guess what the letters meant in our case.
Although when CBS bought KNX in 1938, it also opened CBS Columbia Square studios as its hub of west coast operations. However I agree that San Francisco was a business center at the time, as far as banking, financial services, and advertising. In fact until 1930, San Francisco was more populous than LA.