Gilligan's Island, Julia and What's Happening!! made it into syndication with only three seasons each.Jack P said:I've read the pressure to continue Chico after Prinze's death was because at the time three seasons was not considered enough to get a syndication deal. So money influenced their thinking on that point.
NBC barely had any other sitcoms in 1977 and very few hits in general. Redd Foxx and Demond Wilson both left Sanford and Son for other series on other networks, and that's why Sanford Arms happened and why they were desperate to keep Chico and the Man going without Chico.