So why exactly was this show cancelled?

I thought there was a marked decline in the quality of the writing from season 3 onwards; the show became campier. Also, I thought Teri lost an unhealthy amount of weight in the later seasons losing her voluptuous beauty and healthy glow. I guess it could have been from the stress of shooting the series.

The show was build around the romance between the two main characters, and in the first couple of seasons, the "will they or won't they" dynamic that also drove shows like Remington Steele and Moonlighting. The problem for such TV shows is that once it changes from "will they or won't they" to "they did," a lot of the magic goes away. Viewers who were shipping the characters got their wish, but the story is essentially over at that point -- at least the story that those viewers were watching.

This is not to say the show couldn't have survived; certainly the current Superman & Lois show proves that a show built around a married Lois and Clark can work. But Lois & Clark: the New Adventures of Superman would have had to reinvent itself, and in the process, it might have lost its core audience. Superman & Lois is an action/drama, depicting Superman's struggle to balance his life as a superhero with his life as a husband and father. Lois & Clark was basically a romantic comedy series. As a rom-com show, it really had nowhere left to go, and to have changed into something more like was Superman & Lois is today was probably too great a shifting of gears for the creative team of Lois& Clark to manage, given the lighter tone their show had from its very beginning.

Smallville was drawn out way too long, and I lost interest long before the end. By contrast, this show went off the air before it had a chance to. I'd rather have it that way. It sucks when shows are cancelled before their time, but on the other hand, that means they never jump the shark either.