Put a period on it: A plea to "Big Love"

Some months ago, I had been toying with the idea of doing a weekly recap on "Big Love," much like the ones I've done on "Mad Men," "Lost," and "True Blood." But I didn't, for a number of reasons. A) I didn't really have the time and B) there's just too much going on!
Yes, I realize that I write about "Lost," which is far twistier and more complex than "Big Love." But, while "Lost" is, in many ways, a messy show, it's a controlled mess. "Big Love," with its ever-growing web of plotlines and character relationships, is really starting to spiral out of control.
When it began, "Big Love" was about a man, Bill Hendrickson (Bill Paxton) with three wives (Jeanne Tripplehorn, Chloe Sevigny and Gennifer Godwin). The show was about how this unconventional family functioned, and how Bill balanced his many home responsibilities with running a business (a home improvement store) and engaging in power struggles with the local demigogue, Roman Grant (Harry Dean Stanton).
The show, from the beginning, had a lot of balls in the air. But that was OK. After all, this was the story of a man trying to take on too much. A little chaos in the story-telling was par for the course.
However, over its past few seasons, "Big Love" has kept adding stories and complications. In addition to the wives, the power struggle and the home improvement business, Bill's taken on running a casino and running for office. If that weren't enough, all the other characters have multiple plotlines as well.
We've seen Nikki (Sevigny) struggle with her identity, deal with the discovery of her long-lost daughter, confront waning feelings for Bill and learn that her widowed mother was marrying Nikki's ex-husband. Meanwhile, Margene (Godwin) is running a business, dealing with her feelings for Bill's eldest son, and still trying to claw out a place in Bill's family. And Barb -- look I don't even know what's going on with Barb this season.
In previous seasons, Barb has been a wise mother hen, full of love but also capable of manipulation. This season, however, she's become a bit of a dummy, incapable of handling her responsibilities at home or at the casino.
And don't even get me started on the storylines of the show's many, many supporting characters.
To make matters worse, last night the show added yet another plot thread -- the re-appearance of Ana, who was briefly Bill's fourth wife. Ana, as it turns out, is pregnant with Bill's baby. Sigh.
There's still a lot I love about this show, particularly the acting. The women are all good, with Sevigny a standout as the angry, damaged Nikki. The show also is capable of delivering strong moments, like the harrowing bit from a few weeks ago when Bill forced loyal sidekick Don to out himself as a polygamist for the good of Bill's campaign.
But the good stuff often gets lost in the midst of so many twists and turns. It needs to focus. And, in my view, there's no better way to do that than by setting an end date for the series. When the creative forces behind a show know they have a time limit, they're more likely to pull things together. Just look at "Lost." Look at how much more organized it became once it had an end date. Also, "The Shield," while always strong, had a particular clarity in its final season. And the main reason "The Sopranos" floundered in some of its later seasons was that David Chase and HBO kept delaying their end date.
When will the TV powers that be learn that putting a period on a show's run only helps it creatively? Wouldn't the TV powers that be rather guide still-excellent shows gently to their finish, instead of yanking them off the air when a dissatisfied public jumps ship?