Short answers, pulled from the story.
Lucille Ball and Desi Arnaz invented the rerun during the production of I Love Lucy between 1951 and 1957. They rebroadcasted episodes while Ball was pregnant to fill summer hiatuses that previously featured lower-priority replacement shows.
Rod Serling's teleplay Patterns proved the viability of this strategy in 1955 when a reairing drew more viewers than the original broadcast. People who missed the first airing a month prior tuned in to catch the reairing, buoyed by strong word of mouth.
About 100 episodes are required for a weekly series to be rerun in daily syndication at least four times a week. Few people anticipated the long life that a popular series would eventually have in syndication so most performers signed contracts limiting residual payments to about six repeats.
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 Hallmark Channel all devote schedules to postsyndication reruns. Since the early 2010s digital subchannel networks allowed increasing specialization including MeTV, getTV, Antenna TV, Rewind TV, Catchy Comedy, Roar, Laff, Buzzr, Bounce TV, TheGrio, Story Television, TrueReal, Defy TV, Twist, Quest, Grit, WEST, Heroes & Icons, Circle, Stadium, SportsGrid, Comet, Charge!, True Crime Network, Court TV, Ion Mystery, Start TV, Newsy, Movies!, and This TV.
Perfect Strangers has seldom been in wide syndication since the late 1990s primarily due to lack of demand. Only a DVD set of the first and second seasons was released because of the expensiveness of relicensing songs used in later seasons performed by the show's two lead characters.