"I don't see why it is immoral on its face."
Because $50,000 is a sum that could pay for operations or chemotherapy for human beings that would otherwise die, and the delivery of the funds and the medical services is practical. People are more important than animals.
Is it immoral to spend $50,000 on a watch for yourself, when the same sum will pay for operations or chemotherapy for a human being, and a perfectly good timepiece can be had for, say $500? At least paying for a dog's prosthesis shows caring for a life other than your own. Is it not less selfish than spending thousands for frivolities for oneself?