Perhaps FFG feels that they've hit a wall in terms of additional, unique, interesting content that isn't extremely niche and privvy to lesser known sources, and to develop anything new in the OT wouldn't be gripping enough...aside from Ewoks. If you look at the IA product page, there's already more individual products than with Descent 2e, so there's arguably been more to invest in with IA than with Descent...IMHO, I'd say that it had a good, healthy run in terms of content and was given a considerable amount of attention since it launched. It may just feel like it's being abandoned because it was a narrower time window in which they released everything.
Again. Just my two cents.