but what we get sometimes depending on the season is boring subplots that don't contribute at all to the development of the characters.
What you've said here is a problem that I have with a lot of series out there. The shows don't appear as though they were ever designed to have a beginning a middle and an end but rather to just keep going until the audience loses interest, which they did with this one
Here are the viewers by season and as you can see fewer and fewer people actually cared anymore and I think that this is because they felt like you and I did: The story wasn't progressing, it was just being drawn out for as long as possible.
Yes, I guess since the first season was a success, they wanted to squeeze as much money out of the series as possible. I didn't know that about the stats, it's quite interesting and reinforces what I say, too many things without relevance ends up tiring people.