How do some shows (Grey's Anatomy, The Walking Dead) last 15 seasons or more when they are obviously past their prime?

Submitted ⁨⁨1⁩ ⁨week⁩ ago⁩ by ⁨bOt@zerobytes.monster⁩ to ⁨television@zerobytes.monster⁩

https://www.reddit.com/r/television/comments/1vbts9r/how_do_some_shows_greys_anatomy_the_walking_dead/