I have to disagree with the idea that there would be more sets if "the ACW had been fought in Europe" for one reason: it ain't so.
There were quite a few major wars fought in Europe (and by European armies) during the same era. The 1850-60's were a hot period in European history, and those wars get less figures than the ACW. The Prussians were attempting to unify Germany; Russia was supporting Slavic nationalist abroad; the Italians were fighting for independence; the Austrians and Turks were struggling to hold their empires together. Yet, compared to these wars the ACW is pretty well covered.
Likewise, there were major conflicts taking place elsewhere in the Americas. We've got no figures for the Bonapartists' Mexican Adventure or the multiparty Pacific wars.
Not to mention the Taiping Rebellion, 3rd Opium War, and the Abyssinian War, three significant wars that the British fought in uniforms very like those worn in the ACW.
I don't think it is the ACW that is neglected, it is the whole of the 1860's.