1000 years ago, there were three sea ponies who were born with a slight disability. Although they tried their very best, it was still a very hard life for them. When a unicorn in a funny cloak and hat offers a way to give them what they desired, why would they say no?
Of course, there is a price to pay, but he's only "borrowing" after all. And it's for his home land too. It should be fine.
(cover art under reconstruction)