Why do most series end in a rubbish way?

[Aeleys]

Apart from the ending to the new BSG, I've always been left disappointed by most series at either not leaving it in a good way, or seeming to just stop dead with no 'ending'

Is it just due to them not caring anymore because they know it's the end, no budget etc?

Really annoying.

 

[Aeleys]

It's just really annoying watching many hours of something for it to just be meaningless...

I just got done watching The shield and that ended poorly I was expecting so much more, but it kind of just fizzled out

BSG is by far the strongest ending, and most satisfying I've seen so far, and I'm gonna assume breaking bad will leave me with the same feeling.