They're adding feature updates to support things like new weapons that various customers want to use. Some of those include new weapons that did not exist when the plane was being designed.
Some of it is also feature updates to enable features that were left "for later" because the software was so far behind.
Some of it is updates to deal with problems that were discovered during flight testing. Those include hardware problems (bugs) by the way, not just software bugs.
The plane is technically still under development. The customers (US and UK now) are now flying early models around and reporting back problems to be fixed. Actual normal full production doesn't start for a few years yet.
Biting the hand that feeds IT
