Noon newscasts have actually been around since at least the early '60s, and a TV guide from 1963 I have shows Tulsa's KVOO (NBC) and KOTV (CBS) having them, with the second 15 minutes being more lifestyle oriented, in between the morning game shows and afternoon soaps just like it still is today with CBS. But that half-hour has more or less been the "death slot" if it wasn't moved to another time or station.
Either way, daytime game shows were on the way out by the late '80s/early '90s as fewer people stayed home during the day, and although soaps would remain somewhat popular over the next decade or so (though even those were a bit past their early '80s peak in popularity), the daytime TV landscape was certainly in the direction of news/talk, a lot like what happened to non-music programming on the radio in the '50s, game shows included. In addition, with cable sort of being TV's equivalent of radio's FM band (which also took off in the '50s/'60s), it only meant that the choices were getting more fragmented, and suddenly, the networks had to either to scramble to find more lucrative options (extra news or talk shows), or giving back time to its affiliates. Only CBS today comes close to a daytime schedule from the 1960s-80s.