Well, Schoeller you've answered your own question, shipmate. The Navy kept them because they saw no valid reason to buy a replacement small arm. The Teams in particular use them for their lethality, accuracy, and ruggedness. And when your all out of bullets and are facing off against a hostile insurgent armed with qat and a rusty machette, the M-14 helps make a great crunchy corn-chip sound when used as a club.
Besides, what else could possibly be used as a line launcher during UNREP? ;D
"Anchors aweigh my boy, Anchors a-weigh..."