I know a little about the period leading up to the Napoleonic Wars and a fair bit about the Wars themselves, but I've rarely studied the actual peace process, and this issue sticks out like a sore thumb.

It seems to me that, in the immediate aftermath of Napoleon, leaving Corsica--his birthplace--in the hands of the French state would not have appeared wise. This is on top of the existence of Genoa at the time (to be integrated into Sardinia-Piedmont, but whatever), which had reasonable claims on the island dating back, at the most recent, to late in the reign of Louis XV. So... why didn't it go to them? Or, failing that, why wasn't it granted to Sardinia-Piedmont, given that they did control the adjacent island and could, in a way, be seen as the successors to Genoa's claim?

Was it that the participants of the Congress were unconcerned that Corsica was Napoleon's home island? Were there concerns about the balance-of-power (I find that unlikely from just a single island, but I suppose it's possible)? Were there prestige issues associated with divesting from France a territory which was gained during the reign of a Bourbon King?