Well, the writers' strike didn't help for one thing. We do know that JMS and WB were discussing more Lost Tales before the strike started, but WB didn't pull their fingers out and get it sorted beforehand because they didn't believe the strike would happen.
JMS himself is also now extremely busy building a career in the movies, which is a big change from where he was before the strike.
He isn't desperate to tell more B5 stories, we are just desperate for him to do so. Time will tell whether there is still life in the Lost Tales, or whether JMS/WB have something else up their sleeves at some point in time.
And as far as the TMoS "debacle" is concerned, everything I have read about Hollywood leads me to the conclusion that what happened there is pretty much the norm, and an independent project like that actually getting off the ground, filmed and into the theatres is very much the exception.