Simple answer a zoo holding only surplus males plenty of zoos doing that in Europe and the UK,and who knows what bulls maybe available when TB restrictions are lifted a ready made herd of females able to breed is an attractive proposition.Well if Yoda is just an unwanted expense I suggest we apply the Copenhagen approach to surplus male giraffes!
Not sure how successful that would be with an older in an established herd with breeding experience? Bachelor groups tend to be for animals who are young and haven't yet bred, but I suppose that would be possible. You also have to contend then with a male who would be able breed with both females offspring, as well as the two adult females. Either way, a large amount of shuffling around would be quite likely.
If the "Copenhagen approach", as you put it, was an option, it would likely have happened already!