The MDFC lands were the biggest hit, and Erik's personal favorite designs, so when he was making cards with every mechanic, he made some land MDFC designs
Hightide Hermit: [Category 2] ETB yield is 4 Energy for 5 mana, then you can spend 2 Energy to undo the Defender limitation
The real spice comes from transforming this flip land into The Tomb of Aclazotz, which allows you to recast all those creatures you sacrificed and gives us a rare source of black ramp
Goliath Daydreamer's last ability allows you to cast an exiled card with a dream counter on it only while the ability is resolving and still on the stack
You could make Commander Tax somehow linked to the number of lands, but that would be completely irrelevant in the face of mana-producing artifacts
Because millions of people share similar experiences, older cards continue becoming more desirable