This is why Warrior does not have a passive effect.

It's actually quite simple. It all comes down to how easy it is for AD based champions to clear camps during the early to mid laning phase vs mages or tanks. In most cases a mage will walk into the jungle at the start of the game with single, maybe double digits worth of AP. Also they mostly need to rely on longer cooldowns and insufficient resource pools to dish out their more reliable damage. Lets face it, mages are made to farm in a lane where they can patiently wait for their own minions to absorb and deal enough damage for them to last hit with an auto attack. That simply isn't possible in the jungle. Tanks have a better shot at out tanking jungle camps, but even they don't have enough damage output on their own to effectively clear. AD based champions who are effective junglers not only deal significantly more reliable damage from their auto attacks, which do not require a cooldown or resource, but their abilities often allow for AD scaling on AOEs, DOTs, CC, Buffs/Debuffs, and auto attack resets/empowerment. On average, by the time they have completed their jungle item, they do not need an additional passive to clear camps, instead they are just farming and ganking. Therefor, by giving Runic Echos and Cinderhulk junglers a power spike it helps to catch them up to the Warrior junglers.

Some of you may have noticed that I did not include Devourer. This is because it is a bit of an exception. It also works well AD based champions in the sense that its strength comes from auto attacking. However, the reason why I feel this works well is because it requires the player to clear camps or gank effectively enough to evolve it into Sated Devourer, which usually happens around the time where the laning phase is ending. This means they will get their power spike a bit later compared to the other three enchantments, but when paired with the proper champion and items, this is one of the strongest jungle items, in my opinion.

As always, comments are encouraged. I am also aware that there are likely to be exceptions to everything I said, and please feel free to point them out.