The studios all through the 1940s and 50s had a kind of "gentlemen's agreement" not to release any post-1948 features, or even the pre-1948 major color blockbusters like Gone With The Wind, for television play, in order to try to preserve the value of recent product for theatrical release and (in the case of the blockbusters of the time) re-release in the movie theaters.
Atitudes began to change later after the studios made peace with the networks, stopped looking at them just as competitors and started looking at them as potential production partners when they began selling a lot of series produced by their lots for the networks to air. The big change came in 1961. NBC struck a multi-million dollar deal with 20th Century Fox for the first television release of a large library of their more recent films initially released between 1949 and about 1959, sweetened a few years later by releases from the early 1960s, for a new movie series called simply "Saturday Night At The Movies". The broadcast of relatively recent hits (most all of them in color) proved lucrative for Fox and a big ratings booster for NBC when they hit the air in the fall of 1961, not to mention a significant sales-booster for color TV sets (most of which were made by NBC parent RCA back in those days). The NBC movie deal changed everything, and got the other studios to start licensing network play of their newer films as well. Even today you don't see films less than a couple years old on over-the-air broadcast television unless they're specifically made for TV (another subject worth a separate thread)--the very recent films go from theaters to pay per view and DVD first, then soon afterward to cable, before the networks and local stations take their turn. But the 1961 Fox deal with NBC broke the dam on telecast of films that weren't a decade or more old.
