Here's how I see it:
A Rogue finds a locked box and takes it home.
He sits down in front of his fireplace with plenty of time and absolutely no danger.
He keeps trying to open the box all night, and will eventually succeed. So rather than taking up precious gaming time by rolling the check over and over, he declares that he's "Taking 20."
The Take 20 "fast forwards" the game, taking the place of a bunch of boring dice rolling that would otherwise play out like this:
Round 1:
Rogue: "I roll an open locks check."
DM: "You fail. The box is still locked."
Round 2:
Rogue: "I roll an open locks check."
DM: "You fail. The box is still locked."
Round 3:
Rogue: "I roll an open locks check."
DM: "You fail. The box is still locked."
Other Players: "Oh, come ON already!!!!"
(until eventually)
Round 20:
Rogue: "I roll an open locks check."
DM: "You succeed. The box opens."
It's obvious that the Rogue can keep checking until he gets it right. He has plenty of time, and no distractions or threats. A perfect place to just skip all that dice rolling and have the DM declare "okay, some time passes and you manage to get the box open."
That's all Take 20 is meant to do. Skip over a bunch of dice rolling that would otherwise slow down the game.
Here's why it CAN'T work for Hide.
The Rogue attempts to hide in the forest.
An Ogre comes along.
The Rogue wants to "Take 20" on Hide, but he really can't because this time the Take 20 would be "fast forwarding" past IMPORTANT, GAME ALTERING opposed dice rolling that would otherwise play out like this:
Round 1:
Rogue: "I roll my Hide check."
DM: "The Ogre rolls his Spot check. He beats your Hide check. He bites your head off."
Take 20 won't work with Hide because the Ogre gets to make Spot checks to oppose the Hide checks. If the Rogue gets 20 attempts to Hide, then the Ogre gets 20 attempts to Spot. Take 20 can't be used to change the way a Hide check works, somehow giving the Rogue twenty hide checks while the Ogre only gets one spot check.
Take 20 works with the locked box, because failure means the box just sits there still locked. But failure at the Hide check means the Ogre has seen the Rogue, and now the Ogre gets a turn that might prevent the Rogue from making any more hide attempts for a long long time.
FROM THE SRD: Taking 20 means you are trying until you get it right, and it assumes that you fail many times before succeeding.
Failing the hide check means the Ogre has spotted the Rogue. The Hide attempt has FAILED. The Rogue can't keep on attempting to hide another twenty times, because he's standing there in plain sight, and because the Ogre gets a turn to do something, and that something probably involves the Rogue's blood being generously sprayed around the forest.
Take 20 simply "fast forwards" through a lot of dice rolling that would otherwise slow down the game. But if it isn't possible during normal play to keep making checks until you succeed, then you can't use Take 20 to do so.
If the Rogue can't make 20 Hide attempts while the Ogre just stands there, then he can't use Take 20 to somehow "skip over all the rounds where the Ogre sees me and get to the round where I successfully hide."