Just a theory of mine, but perhaps they only gather to breed in the wild every 2 to 3 years and that's why they refuse to lay the eggs. Also it could be that they travel to the same exact spot where they were born like a lot of other animals do and this task cannot be performed in captivity so the female refuses to lay.

Just a theory with no scientific proof to back it. So little is known about this species in the wild so it would be hard to say exactly why the females refuse. It is a possibility. Bullfrogs return to the same pond where they were born most of the time so its not a far stretch to assume this possibility as well.