Here's a start---

      So, Migu, I read the dialogue of____ on Soft power.

    The most obvious and direct answer--and Drew brought it out himself--is  that « soft power » is indeed in use constantly by the US and all other governments.   When it works,  you don't see it except via indirect indications.  The professionals who are involved, however, see the effects of the closed-door discussions, the back-channel dialogues.   These are literally daily  phenomena.  « Soft power » is in use whenever high-level talks produce a trade-off, a quid  pro quo between governments.   Trade agreements are soft power; development aid, foreign loans, investment in foreign capital and infrastructure; the granting of memberships in international bodies; the relaxation of barriers; cooperative scientific research; all of these, or, conversely, their denial, are elements in soft power tactics.  There are of course other sorts of  incentives--direct  bribes in cash or resources, the offer of military cooperation; espionage intelligence sharing; technical assistance in areas where a  nation is particularly needy.  The only reason to look upon it as somehow sinister in nature is that it is so often so largely un- or under-reported  and that the interests being so well catered to are the same largely or exclusively corporate ones which happen also to give so generously to political campaigns--nota bene: both Republican and  Democratic party campaigns.

    The one thing that I'd stress in difference to Drew's picture is that the Democrats as office  holders, and as governing  administrations are in no way strangers to these habits.   This  goes on administration in and administration out, without regard to political party.  Differences of emphasis occur as when, for example, the senior Bush administration came into and then left the White  House and  then returned again in 2000.   With each arrival of the Bushes,  the Saudi Arabian regime found itself once more in a relatively more privileged position vis-a-vis the people in the White House.

    I also agree with Drew's view--expressed variously by the difficulty of pinning them down as neatly definable--concerning the fluid character of these « interests » of the U.S.  

To follow your line of  quesioning, then, you would like to know why it isn't used more, or, ideally, why it isn't used exclusively.

 For that there are numerous possible explanations; but the most obvious to me is that there are a number of "interests" which simply don't lend themselves to being pushed and achieved by soft means.

 In particular, there are the too frequent and recent examples of Uncle Sam whipping forceful discipline--or trying to on those of his wayward erstwhile obedient client-state tin-pot dictators.  With these, the "soft" techniques have been tried and proven ineffective; then Uncle Sam gets really, really angry.

But that is only the first example I can think of.

  More, perhaps, later, if you're not satisfied with this response.

  I also agree with Drew's observation that, in general, the great majority of Americans are simply not interested in or aware of or informed about international political affairs.  It's already more than they can manage to interest themselves in their own domestic political affairs !

"In such an environment it is not surprising that the ills of technology should seem curable only through the application of more technology..." John W Aldridge