We don't need ASW platforms anymore, since the USSR collapsed.
/sarcasm
That does seem to be the theory.
Of course if we really are detecting these subs by some yet unknown, more or less, method, but which we don't want to expose, for obvious reasons, we still have plenty of ways to sink 'em, if and when the time comes. Why show our hand now?
For example, I seem to remember reading something about using radar or other sensors on satellites to detect the disturbance, (displacement of the water by the sub) caused by a moving sub.