Several reasons. One is sentimentality. But, well beyond that is the airworthiness of the aircraft. The P-3 is over 50 years old and has had the crap beaten out of them. And, the Chinese don’t need to force anymore P-3s to land in China.
As things stand today, there are so few P-3s still on active duty that they have all been assigned to the Fleet Air Wings, not the sqaudrons. The replacement P-8 is too expensive for the Navy to be able to purchase enough to replace their geriatric P-3s. I dearly love the P-3 and have very fond memories of them but, let’s be honest, they have earned their rest and should be retired with the dignity they earned.