The good thing about poplar, is that it's cheap, local (here in the East), plentiful, workable, accepts a finish well if it's sanded right, and while plain, under a solid or opaque finish can look good. It's nice to make a body out of the kind of wood that grows in your back yard.
As for Alder, a lot of the same can be said ... I've seen some nice pieces with interesting beauty marks, that look great under an opaque or translucent finish.
Sure, neither are figured Korina, or flame maple, but with a little imagination they can look real nice.