@DacenOctavio: Might be a matter of wanting the sacrifice outlet to do more than just sacrifice+a scant 1 life (is it just that the Claws and Market can be deployed cheaply?). Mostly a matter of getting all one can get in the process. Although that said, I think I'd prefer something like Fanatical Devotion or Martyr's Cause in this scenario, compared to the Boneyard (think persist, EtB, and things like Deathrender all put together). As to Miren and High Market, maybe they don't want any colorless-only lands, for some reason. At least, that's the best explanation I can think of.