Well for one he is the personification of the alliance between The Kingdom of France and the United States. This alliance was key in supplying the American revolutionaries with badly needed supplies and money. In February 1779 after fighting with the Americans he returned to France to help lobby for an increase in french aid. This lead to the dispaching of a french fleet as well as 6,000 men under Comte de Rochambeau. This french fleet was very useful to the united states cause most importantly blockading Cornwallis in Yorktown leading to his surrender and helping to end the revolution favorably to the Americans. This lead him held in incredibly high esteem by the notables of the newly free United States

By being a foreign born leader with no particular ties to any state he could act as a somewhat unifying figure. After the revolution he did a number of tours of the states which helped increase his already considerable popularity, leading to a number of honors, one of which was Maryland making him and his heirs "natural born citizens of the state" letting him boast that he was an American citizen before he became a french one (the concept of a citizen of France itself was not to come to the front until the french revolution).