Liberia was an Independent country for more than a century before the Compact of Free Association was even thought up as a system. Palau, Micronesia and the Marshall Islands got them because they're tiny collections of Islands the that the US ended up with following the second world war. The reason they exist is because those three nations could use various US domestic services and didn't particularly have the ability to build them from scratch. The US logic about it was due to the view that "They're a bunch of Islands, we should be nice."
Liberia on the other hand, doesn't really have anything on common with the others besides the fact it was the quasi-colony of the United States owned by a Private Society up until 1847. Are we talking about having the US embrace it as a colony back then or something else?