I'm not sure we really should call reruns "dead" but the game has changed. Televisions's distrbution of older material went down towards the tale end of the 90s and the early 2000s because they had to compete with the internet. They used to count on people sitting around watching tv for long periods of time as a given. It's how lots of us got most of our pop culture, In those days television channels had tons of reruns and wider schedules.
It was also because of the usual cause of extinction-- Destruction of Native Habitat:
Before cable, growing up in the 70's and 80's, a local station ran Bewitched or Leave it To Beaver reruns at 4:30 because, well, they had to show SOMETHING. There was probably a housewife audience still watching, and kids were home from school; the network game shows ended at noon and the network soaps ended at 4, so stations were left to their own devices until the pre-news came on at 5-5:30. Distributors sold packages of reruns, movies and syndie series to local stations, just so they could have something in their arsenal to show.
Syndicated TV burst out in the 80's, which gave us afternoon cartoons in the 80's and Jerry Springer and Judge Judy in the 90's. Nowadays, The View spun off enough morning variations to keep network affiliates going from the morning shows to the noon-hour news to the network soaps and Dr.'s Oz and Phil carry the 4-5 hours.
Used to be, local stations aired their little home-stocked collection of rerun/movie ephemera during the afternoons and late-nites, or made their own local area programming (local affairs, interviews, cooking, bowling, Bozo kid's shows, etc.) Now, with so much station programming handed to them on silver platters--even the wee hours are filled in with all-night network news--local stations have no reason to use their soundstages for anything but the news division anymore. And if a vacancy shows up at 4pm....we now get the Early News at 4.
Of course, we didn't worry, because cable exploded in the 80's with dozens of little niche channels that needed old movies and reruns to show, so we thought they'd take care of that outlet for us. Oh yeah, we sure thought THAT, didn't we?...