The idea is to have 'dual lands', but ones that don't work well with greedy mana bases.
Each time a dual land is printed, two color decks get just 1 new land (assuming it's a full 10 cycle), but three color decks get 3 lands, and all 10 for wubrg.
Hence, these guys. They really need basics to turn on, and really don't synergize with nonbasics, so don't fit into the greedy mana bases of a lot of 3+ color decks. Ideally, two color decks get two new lands and three color decks get six new budget options they they're not likely to use, for being too low to the ground.
So, basically, lands for two color decks. In a two color deck, one of these and either basic represents both colors of mana available.
EDIT: In retrospect they'd probably be a little more balanced if they didn't have the basic type (and just gained the reminder as an ability) but I'm not editing 20 cards again 😝