How does the writing for shows like this work?

We all know the writing was the weakest part of this show. So how does that happen? I would think that if you are investing millions into a new show, you'd want the best writers and a team to make sure that you have a solid agenda for every season with as few inconsistencies and plot holes as possible.

Currently I have two shows that I watch, and one is losing its footing. Doctor who is an awesome show that I cant see how it can get old. And Fringe, which seems to have run out of ideas and may soon kick the bucket.

It seems to me that all the recent scfi shows suffer from terrible writers. Terra Nova is probably the biggest offender, followed by the Walking Dead(Yes! It has terrible writing!)and Falling skies. TWD I watched for awhile before the huge character flaws and terrible plot devices became too much, but Terra Nova I couldn't even finish the pilot episode it was so horrendous and falling skies, as much as I tried to like it was the same damn dystopian human survival show we've seen a thousand times except the last remaining humans are dumber than a youtube comments page. What ever happened to characters with character and flawed characters having redeeming qualities? In BSG, even the most despised man in the entire show had qualities about him that made you want to watch him, not repulse you like every character in V.

So where have the writers gone? What happened to the days of BSG, Firefly, Farscape, Stargate, the Outter Limits, Star Trek, The X-Files and so on? Are we just in a creative lull or our the golden years of scifi behind us?