It's possible that an "off-cycle" order could come through, meaning that the series could be filmed and either held until the following season or used as a midseason replacement.
The CW reportedly believed that the project simply needed more time; nothing in the report indicates that there was anything particularly wrong with Amazon. It's likely that after the recent, failed David E. Kelley Wonder Woman pilot, everyone involved just wants to go slow and get it right.
Back in November, network brass expressed that the script looked good but was not yet complete and that they were beginning casting. Neither a final script nor a principal lead has yet been confirmed for the pilot, so it's possible either or both are not ready for prime time.
Tomorrow People, a new drama about everyday people with extraordinary powers from one of the producers of Chuck, was ordered. The Selection, one of this year's pilots that wasn't picked up and a show that has been widely compared to The Hunger Games, was also sent back for a second pilot.