Posted by torcan on March 26, 2012, 7:37 am, in reply to "Re: 40 Years Ago..."
I'd guess that there were no more scripts to be done that season. It was the 26th episode of the season, and by the early '70s TV seasons were shorter anyway. Most shows did around 24 episodes per year by then, so I think 26 was likely that season's order.
Even though it wasn't offically a "finale", I always thought the last scene was a good way to end the series. In some ways, it sort of is a "finale" - to me anyway!