Because it's cheap and easy to run. Generally barter. They don't pay anybody to run it. Just run the network or show's ads and it's good. Weekends are generally times when nobody is listening. The only shifts that really matter are Weekday mornings, middays and afternoons.

As for the Talk stations, that's how they make money on the weekends. Most of them run syndication and those shows don't air on the weekends. They have to make money somehow.

A lot of the bigger stations run by iHeart, Audacy or Cumulus have a syndication company that is co-owned or they produce syndicated programming. iHeart owns Premiere Radio. Cumulus owns Westwood One. Audacy is involved with much of the CBS Radio Network. Running it clears it for a market so they can say to advertisers it airs in this market.