Yes, other things are preventing the novels from going forward though they didn't get into them. Shadowrun novels have been going to print. But timeline was one of the reasons. It was mentioned that the WizKids Dark Age novels just didn't sell well. Maybe another reason.
Interestingly enough, while the new German novels Ulisses Spiele is producing sell well (at least in E-Book format) the translations of the Dark Age novels didn't. So they stopped translating them about a month ago and will now produce more new German novels.
Personally, I think the Dark Age novels had problems, because they had a very poor start. You could read the first novel, but then had to pretty much skip the next ten to get to anything you wouldn't want to pull your eyes out while reading (and that's even without the Proving Grounds Trilogy that I can't describe here without breaking dozens of forum rules).
I simply cannot imagine a lot of people fighting through all the bad novels to get to the good ones. Most people will never find out, that it gets better - a lot. Dark Age novels didn't have an era problem, thy had a quality problem during the first dozen novels and never recovered from that.
The novels Ulisses is producing are set in a lot of different eras, so people obviously like to read BT and don't care much about
when the novels are set. I'm currently writing a
six part E-Book cycle for them set in the Jihad era - which will be a first, even for the German novel line. Let's wait and see how that one will go, but I assume it will sell just as well or even better than the novels set in other eras - the Jihad is undiscovered territory after all, as far as novels are concerned. :)