My only guess at the moment is that it is probably due to commercialization reasons, and also maybe lack of a partner to facilitate that. But still, it is odd to me.
One idea:
Considering the complexity of the EU market: - lot of countries, local authorities (top of "central" approval) - longer commercialization (deals / prices should be agreed country by country)
They could not reach a deal that could be ending by end of 2018 (Like KOWA in the US). Existing deal in 2019/2020/… decrease their flexibility going forward.