Honestly, Freddie's boring. Really good, of course, but good in that steady, professional, unspectacular way. By the end of the year he's going to be between .290-.300, between 20 and 25 home runs and around 100 RBI as a good-but-not-great defensive first baseman. He doesn't run fast, he doesn't hit massive home runs. He just hits his line drives to left-center. That's not a recipe for a good nickname.
Besides, "Freddie" is one of those first names that's mildly goofy enough that a nickname isn't necessary.