Hearthpwn

The better question is, "why shouldn't it be a card?" There are way worse cards than recycle in the game (Kidnapper), whether or not it has the appropriate cost is a fair discussion but questioning whether or not it should exist doesn't seem useful.

Druids are not known for their hard removals which is why Naturalize and Poison Seeds have high consequences which is why the other hard removal spells you mentioned are better quality

Look at it similarly to M:TG. Green had the big stompy minions that blew others out of the water, whereas blue had the incredibly powerful instants and sorceries. When blue started getting the powerful creatures as well (like delver of secrets) blue became overly powerful (even more than it already was) and it was over represented in standard format tournaments. If druid got recycle as a 4 drop, or some other powerful hard removal spell, I guarantee you people would play druid far more than any other class.