Short answers, pulled from the story.
Lucille Ball and Desi Arnaz invented the modern rerun while Ball was pregnant with their second child in 1951. Before this moment, television networks simply went on summer hiatus, replacing their popular shows with lower-priority filler programs.
Rod Serling's 1955 teleplay Patterns provided the final proof of concept, drawing more viewers in its second run than it had during its initial broadcast. This phenomenon occurred because audiences who had missed the first airing a month prior tuned in to catch the reairing, creating a word-of-mouth effect that networks had never anticipated.
Generally, about 100 episodes, representing four to five seasons' worth, are required for a weekly series to be rerun in daily syndication at least four times a week. Very popular series running more than four seasons may start daily reruns of the first seasons while production and airings continue of the current season's episodes.
This situation remained unchanged until the mid-1970s when contracts for new shows extended residual payments for performers regardless of the number of reruns. Most performers signed contracts that limited residual payments to about six repeats, after which they received nothing while production companies kept 100% of any income.
Channels that devote at least some of their program schedule to postsyndication reruns include Nick at Nite, TV Land, TBS, USA Network, WGN America, Logo TV, Pop, Discovery Family, Game Show Network, Boomerang, Nicktoons, INSP, fetv, RFD-TV, and the Hallmark Channel. Equity Media Holdings had been using low-power television stations to carry its own Retro Television Network in various markets, but those stations were sold to religious broadcaster Daystar Television Network after Equity went bankrupt.
The series started to gain traction once the BBC decided to repeat it in a different timeslot, and The Office went on to be an award-winning and critically acclaimed show which has regularly featured in lists of the Best Sitcoms ever. In 2019, the series was ranked 6th on The Guardian's list of the 100 best TV shows of the 21st century.