Personal sympathies aside, after Britain prevailed, the Reagan Administration had no desire to punish the Junta for the aggression.
14 US officials were indicted including the Sec. of Defense, Director of the NSA, and the National Security Advisor. President Bush pardoned most of them.
https://fas.org/irp/offdocs/walsh/summpros.htm
Looking back to that time from my own memory, I don’t think most Americans cared to be honest. South America has always been fairly low visibility to the United States public. In the 1980s the countries that I think had higher visibility in the Western hemisphere would be Panama / El Salvador / Nicaragua. Nicaragua because of its association in the Iran-Contra situation, El Salvador because human rights abuses there (for whatever reason) seemed to get far more media attention than Argentina, and Panama because of our interests in the canal + we ended up actually invading Panama and arresting its leader.
One issue that American liberals had during the Cold War, in terms of trying to raise awareness of “bad things” that U.S. anti-communist allies did in developing countries is a huge and endemic American indifference to foreign affairs. Most Americans would be making little more than a guess if you asked them to label Brazil and Argentina on a map. On some meta level if you could get through to someone and explain the scope of many human rights abuses we tolerated solely for anti-Communist reasons, a lot of Americans would probably have been against them. But the issue was you had to penetrate, in many cases, through a very thick veil of indifference towards the affairs of other countries, a nightly news broadcast which was many Americans’ only exposure to news at the time just isn’t a good format for doing this.
The volume of US arms sales to Argentina both prior to and after the Falklands was pretty insignificant in any event. There’s a RAND paper pdf here titled U.S. and Soviet Relations with Argentina: Obstacles and Opportunities for the U.S. Army published in 1989 which has a table of the value of arms transfers to Argentina on page 69 in 5 year chunks which overlap. For the last 5 year time period of 1982-86 US sales are firmly in last place with $60 million, outdone by France ($80m), ‘others’ ($420m) and the FRG ($1,200m). Going back to the prior 5 year period illuminates both the paucity of US arms sales and something oft forgotten, namely that the UK was a more significant supplier of arms to Argentina than the US prior to the Falklands. The 5 year period of 1981-85 again sees the US dead last at $40 million, outdone by the UK ($90m), Italy ($110m), France ($230m), others ($530m) and the FRG ($1,200m).
The first significant US arms deal with Argentina after the Falklands didn’t happen until 1998 with the sale of 36 A-4AR Fightinghawks for $282 million.
The public impression that the US was a bigger seller of arms to Argentina was probably compounded by the widely reported fact that the General Belgrano was the former WWII cruiser USS Phoenix.
That in great measure because of the perception c. 1980-82 of a high risk of actual American “boots-on-the-ground” intervention in Central America if the insurgencies in El Salvador/Guatemala/Nicaragua escalated, not an unreasonable perception because of there being history of that sort of intervention well within living memory, and of it being highly publicized that the Rightist side was getting support from the American military/intelligence apparatus and the Leftist from the Cubans, so being less than 10 years post-Vietnam you could imagine people thinking, “uh-oh… not ‘advisors’ again…”
Thank you for your RAND paper showing how much Argentine spent on arms purchases from some European countries during the period of 1982-89.