There's a lot of buzz on the internet about how captive killer whales' collapse, but the same phenomenon happens in wild killer whales too.
Researchers don't yet fully understand why this happens, but it seems to be a natural process linked to the whale's unique lifestyle, and a structural protein known as collagen might have something to do with it.
Collagen exists in various types of connective tissue, but it's also abundant inside of whale fins. Whenever this collagen breaks down, the fin appears to go limp. Unfortunately, there's no conclusive explanation concerning how the collagen breaks down in the first place.
One theory suggests that the temperature of a whale's environment breaks the collagen down, but another suggests that captive orcas can't swim fast enough to exercise their fins.
All theories aside, these circumstances seem to vary from one killer whale to the next, whether they're captive or wild. That said, there's an ongoing mystery regarding the subject, and it'll take more research to solve indefinitely.