That's a weak answer. Just put it out there, let other people maintain it.
Not that I'm saying they have to release it (I respect their right to do whatever they want with their own work), but as far as reasons to not release something, that's pretty weak.
Hi,
Thanks for your interest in Grove.
Unfortunately we won't be open sourcing the code due to the time and effort it would take to prepare and maintain it.
Thanks for understanding,
Leah