It sounds like for the USDA at least it's partly an unclear authority issue:
"Vaccinating the mink [...] or reimbursement for depopulated animals requires USDA to establish mink-specific regulatory authority and dedicated programs for HPAI response in mink."[0]
But nonetheless, what a supremely stupid way to die.
[0]: https://virological.org/t/preliminary-report-on-h5n1-highly-...
just a tiny bit insane considering that every time a virus survives a host it mutates to try again a different way and that's how you get species "zoonotic jump"