Why stop there?
Hmmm. . . . . .
At first I thought: low-hanging fruit. They had gotten all the ones that are easy to do, especially since the form turns on the temperment. Which I think is still going to be true. . . .
On the other hand, there are shape-shifters of this ilk in fairy tales with no backstory, and some from families of shape-shifters, still others feature as a Mad
And, of course, for those in the know, there's the trade-off between the liberty of shape-shifting and the ever-present peril of captivity from the cloak. Would they want to? Though they might want to give the Mad Wizard's daughters a means of escape. . . .