For the time the show wasn’t that bad. (the original)
I mean look at any show from back then. The production values weren’t very good compared to today’s. There have been a lot of advancements in the craft, although the acting and story lines have plummeted in recent times.
TV shows today can have the budgets of movies of old.
Sometimes that is just for the cast in later seasons and some of that is for other production elements (sets, locations, soundtrack, etc.).