If I was the passenger I’d want to know it’s found and have the possibility of finding the finder. Best would be to post it online like this—I’d see it that way. If they turn it in to the airline it’s probably going to be stuck in bureaucracy for months. If they turn it in to the NTSB, it’ll be gone for years.
If I wanted to reach out to the owner, one could just open the phone app on the already unlocked phone and call anyone that seems like a close relative. Hoping for the owner to just randomly stumble into an internet post seems very impractical, considering that the phone likely contains a substantial amount of info about the owner.
Besides, why would the NTSB hold onto the phone for years? It's not part of the aircraft, there's no real reason why they'd need to have it at all. Is it just common with US government agencies?