Ships have a certain lifespan, otherwise they start to break down and the hull weakens, which is not really very good. Especially given that many of these ships would've had tough wartime/early Cold War lives within the USN.
A ship as thin as a destroyer, well, after 50 years' service you'd not want to hit a storm.
I was under the impression the FRAM vessels were kept largely as carrier and convoy escorts, since most USN funding during the 1950s/60s went to carriers, nuclear cruisers and submarines. So they were pretty much configured for ASW duties in the Atlantic: since they'd be escorts and also had ASROC they didn't really need a helicopter, but a small helicopter like the RN Wasp or the French Alouette would've sufficed better than an experimental weapon. Or go the Canadian route and rip out half the deck to land bigger helicopters.