Why does Santorin go Purple Smite - CInderhulk on every single jungler?

Basically, that's the most reliable, efficient Smite/Enchant combo in a vacuum. Going, e.g., Warrior or Stalker's puts you under pressure to get off ganks in order to justify your investment. Otherwise, Ranger's gets you to your late-game more quickly, while Cinderhulk is the best enchant in that late game. (Cinderhulk is much more efficient than the other enchants in the late game.) Santorin likes the hard-farm playstyle.

As far as Eve goes, well, she only brings a lot of pressure in the early game, and most pros build her tank/utility from second-item on. Building Cinderhulk instead of Warrior trades off some of the power of her early game for a better late-game. Also bear in mind that tank/utility builds are generally more effective in pro team play than in solo queue; you should probably be building Warrior Eve (or Runeglaive Eve?) in solo queue.

Cinderhulk-Eve is actually pretty good since you can go Triforce and have the rest of your items be defensive, while dealing pretty good damage. Enchants like Warrior and Runeglaive are for when you think you can snowball a lead and finish the game quickly.