I think for a large part, people are willing to forgive a substandard release now and again. The fact that nothing was in the pipeline to potentially make up for Faramir hurt the line more than Faramir did.
By the time the Hobbits came, it was too late. And at an price increase it was too much to bear.
That's it, in a nutshell.
The Faramir fiasco (horrific paint apps) created an uproar that Sideshow didn't squelch by at least announcing a new figure. That would have helped quiet down the negativity and sooth the collector's anxieties over the line.
So with no news coming from SS, people started jumping ship to other lines and companies that were offering a more moderate release rate.
Then, as mentioned by ProgM., the sticker shock caused by the hobbits caused even more bailing from the line.
I still say that if there had been more emphasis in this line from the get-go, and announces/releases had been made at the same pace that the Star Wars line was initiated at, this line would have prospered. I'm sure that for every Faramir, we would have had a fantastic Saruman, Gimli, Ringwraith, Easterling, Gondorian, Rohirrim, etc...
This line had SO MUCH potential, in terms of characters... sigh..