Sets had lower print runs back in this era, and many copies will have been lost or damaged over time
Mill decks are basically required to run graveyard hate, otherwise you'll end up kingmaking Graveyard decks like Meren of Clan Nel Toth which will be delighted with you setting up their deck for reanimation, but you can still run targeted removal like Shred Memory to stop reanimation and leave enough cards in the graveyard for Drown in the Loch to be reliably awesome
Modern-day iterations of these Dual Lands will have some type of drawback to using them, either by paying life for them to come into play untapped like the Shock lands, or more commonly, not having a basic land type associated with them
Undergrowth Recon has to be absolutely busted in some Commander combo I dont know about yet
Topdecking an MDFC land in the late game is awesome, be it in Limited or Constructed, and it gives you more possibilities of sequencing the lands in the early game, while not being overpowered like some adventure cards