C-130's don't fit the marritime patrol role. They do not have the manueverability of a P-3, there's no place to put PSLT's, no room for a bomb bay (and torpedoes HAVE to be carried in one), no place to put some of the sensors.
And it's STILL a 45+ year old design. There's much better, more reliable materials, engines, and methods of construction out there that we should be using.
Thanks for your comments. It's a little hard to understand the part of your comment where you say the C-130 doesn't have internal room for needed weapons and equipment. A C-130 interior is cavernous compared to a P-3, isn't it? And since C-130's are still being manufactured today and will be very widely used for decades to come, it's hard to see how the design can be too obsolete.
Maybe someone will argue that the C-130 is too big to perform the role efficiently -- I think I could believe that.
I'm not trying to be argumentative -- I hope I don't sound that way. Just thinking out loud. (And since I have some affection for the C-130, as a paratrooper, I wouldn't mind a reason to keep the production lines open).