Lost in Space versus The Avengers

I believe, at that time at least, that a show had to be doing pretty well at the three year mark in order to get renewed. I think it's largely because TV contracts typically lasted 3 years. If you renewed at that point, the show was going to cost more to produce because the people involved were going to be negotiating for more money.

According to one of the 20th Century Fox executives, another factor was that Irwin Allen failed to deliver the season 4 scripts/outlines that had been requested (probably by the Network). Certainly he would not have been expected to deliver a season's worth of scripts, but the powers that be would probably have wanted to see some strong ideas to give them confidence in a 4th season.

There's one potential 4th season script floating around - something called "Malice in Wonderspace" by veteran LIS writer Carey Wilbur - but the first draft of that script is dated Halloween 1967, so it seems more likely to have been a third season script that was never produced.

Allen may have been unwilling to invest in season 4 scripts because the writing was already on the wall for the show. I've seen it suggested that Allen was unhappy with budget cuts that the show would have to endure if it went to a 4th season - so, in that scenario, it was Allen who pulled the plug and not the network.

I thought Batman was blamed for ruining LIS viewing figures? While The Avengers became another camp and colourful show, I assume it targeted a more adult audience at the time.

Anyhoo, S3 of LIS proves the show had run out of steam. The proposed new gimmicks for the never made S4 were just awful. While I enjoy most of S3, did anyone need more LIS when it ended? The show had collapsed its focus to just Will, Dr Smith and the robot, and the simple minded scripting of the 1960s wasn't going eke out anything more of worth from their relationship. A spin-off would have made more sense than a straight S4.