It's an old story, dating back to...a long time ago. I think it really became big during the X-Files -
TV shows with arc plots.
But not just that; when the show has been going for a while, developing a large and complex back story. Little inconsistencies begin to creep in between the episodes, flat-out errors appear, and you begin to wonder...
Are they just making all this up as they go along?
You - or at least most of the viewers - watch a show hoping that the creators are weaving an interesting tale to draw you back each week. That's the idea - fill it full of mysteries that the viewers want an answer to so they'll keep watching.
But with the X-Files the answers didn't come. People got bored. And they got pissed off when things didn't make sense. Suddenly you've lost the 'hook' for the show, as people realise that there are no answers. There never were. The writers didn't have a history all planned out.
Take Lost. One of (I'm not saying the only) reasons people watched was to get answers to the mysteries.
The pilot, the creators admit, was pretty much made up without any thought to resolutions. I think it was part-way through season 3 that they realised that they had to stop introducing new stuff because it was cool and provide some answers before people became annoyed a la X-Files. But even then, whether you liked the finale or not, as you sit and mull it all over after wards you don't think 'well, that was a great journey' you wonder 'why couldn't any babies be born?' or 'what was the horse all about?' or any number of other things that weren't answered.
And then there's Babylon 5. JMS planned out a 5 year arc at the beginning. And, despite everything, he achieved it. It wasn't exactly what he set out to do, but it was pretty damn close. He thought ahead and realised that actors come and go and thus every character had to have a 'trapdoor' available so they could be written out if necessary (which happened on a few occasions).
Babylon 5 wove a rich and complex tale, covering thousands of years, with a beginning, middle and end. If this relatively little show could achieve it, why not some of its bigger TV brothers?