They come by the bucketload because you have to sacrifice them
It adds a very Fire Emblem-equse system to the game. Except instead of them dying forever in battle you'll be forced to have to eventually start killing off your lesser used characters in order to power up the souls of your more used ones.
And who knows? Maybe eventually you'll run out of fodder and have to decide amongst units you really LIKE. DUN DUN DUN.