These cost 1 mana to cast and 2 mana to sacrifice, but when you do, you get a card and the mana youve spent to crack the egg
Think Salamence, Dragonite, Reshiram-GX
This is especially true in Commander, where you only have a one-in-a-hundred chance of drawing the specific card you need each turn
These big splashy spells can win you the game on the spot, and are popular win conditions even in decks that dont have Reanimator as the primary strategy
Pushing the impactful cards to higher rarities helps make the games more even-keeled in Limited because of card as-fans (the rate at which a certain card or subset of cards show up within an average booster pack) and in casual Constructed because of card availability
Kodama of the West Tree Green has plenty of ways to modify creatures, making Kodama of the West Tree a solid option for a mono-green commander