Some of that is to retain flexibility, some of that is because it's not a use of resources that serves the product in important ways. In general, the MtG creative team does not make maps of the planes. How are the Dungeon Master Guild's schools of Summoning? I've seen at least a couple on there but I haven't bought any of them yet pending reviews. Any other schools of magic that are thematic to Magic the Gathering besides Planeswalking? You know schools of magic that would be accessible to level 1-10 characters? I think the Unearthed Arcana article Psionics and the Mystic has Blue mind magic all sewn up.

Are there any official or fan made maps of the floating continents of Zendikar? And speaking of Mechanus, I was thinking of writing up a wizard school of Hieromancy (using the fixed damage rule from Mechanus) and maybe one of Pyromancy (maybe base it off the 4e pyromancer mage?). I am intrigued about adding these other MTG planes to the D&D cosmology so that someone could conceivably cast Planeshift and end up in Theros or Ravnica instead of just Baator and Mechanus. Well Innistrad by way of Curse of Strahd. So WotC released that Planeshift: Zendikar treatment, it was kinda rough but it was useful to my purposes since I am running an Innistrad game at the moment.

Planeshift pdf