Short answers, pulled from the story.
Lucille Ball and Desi Arnaz are generally credited as the inventors of the rerun. They first used rebroadcasts for I Love Lucy (1951-57) during Ball's pregnancy, replacing the summer hiatus practice of airing lower-priority replacement programs.
Rod Serling's 1955 teleplay Patterns is credited with proving reruns' viability. Its rerun drew more viewers than the first broadcast, as people who missed the original airing tuned in to catch the re-airing roughly a month later.
About 100 episodes, or four to five seasons' worth, are generally required for a weekly series to enter daily syndication airing at least four times a week. Very popular series exceeding four seasons may begin syndicating earlier seasons while new episodes continue to air.
Early agreements between British broadcasters and the actors' union Equity limited programs to only about two broadcasts within a fixed period such as five years. Once those rights expired, broadcasters saw no further use for the materials and routinely destroyed them. In the United States, many early shows were never recorded at all, since most television in the late 1940s and early 1950s was performed live.
Barter syndication is an arrangement in which a television station receives a program for free in exchange for airing a set of advertisements bundled with it. The Program Exchange was once the most prominent barter syndicator in United States television. Free ad-supported streaming television services now rely on the same model.
Game shows age poorly because inflation makes their prize values look dated over time. Reality television struggles in reruns due to high cast turnover, loss of suspense, and lack of media cross-promotion. Scripted comedies and dramas, described in the industry as evergreen content, hold their value far longer.