Why is it that every time I turn around Marvel is taking away Juggernaut's power?  My theory is that they want Hulk to be the unquestioned "strongest there is" and with Juggernaut at full power there would always be a question.  What do you think?

I agree Juggernaut has been depowered but I doubt Hulk has anything to do with it considering the introduction of Sentry, return of Thor, and the Hulkification of Hulks entire supporting cast (Red Hulk, Red She-Hulk, Skaar, etc).  If they were worried about challengers to Hulk those developments would not have come about.

I think its because when Juggernaut is completely indestructible he's a suitable villain but kinda boring. They've been trying to turn him into a kinda anti-hero or something so having him be unstoppable and indestructible is even more boring.

His full power level is completely unfeasible. He should NEVER lose to anyone below Cosmic level. It makes sense that he be depowered. Though his current power level is too low.

It's not a conspiracy. It's hack writing. 
 
The reason we don't see The Juggernaut doing what he did for decades. Namely show up in somebody's book and kick their asses. And many times just get away with it. Is because these writers nowadays get so fucking butthurt over their pet project character getting made to look bad. 
 
The clearst exampel of this would be Greg Pak. Chris Gage repowered The  Juggernaut in WWH: X-Men. And even made this "Strongest Hulk ever" look rather bad. He was walking over everyone else. But Juggs smacked him around a bit before Hulk ran off. So what happens? The first chance he gets he has Juggs show up in the Hulk comic. And what happens? Not much. The Juggernaut throws a few punches and mostly stands around waiting for Skarr to do something after that. And the fight ends with Skarr launching Juggs into space. Wow great lessen learned there. When what he should have done was use Skarr getting his ass kicked to teach him a lesson. No instead he wins the fight by BFR. Juggernaut looks bad and Skarr looks better than he is. 
 
Then on top of that Pak continues to bring The Juggernaut up in the most dismissive ways possible several issues down the line. We get it Pak. You are throwing a hissy fit about The Juggernaut. 
 
Combine the butthurt with some writers inability to do any basic research about the character. His motivations for one. And well. They just can't figure out what to do with him. So instead of making the stories fit the character they just change the character. 
 
Mike Carey is the only writer that I have seen absolutely nail Cains character in years.

" It's not a conspiracy. It's hack writing.   The reason we don't see The Juggernaut doing what he did for decades. Namely show up in somebody's book and kick their asses. And many times just get away with it. Is because these writers nowadays get so fucking butthurt over their pet project character getting made to look bad.   The clearst exampel of this would be Greg Pak. Chris Gage repowered The  Juggernaut in WWH: X-Men. And even made this "Strongest Hulk ever" look rather bad. He was walking over everyone else. But Juggs smacked him around a bit before Hulk ran off. So what happens? The first chance he gets he has Juggs show up in the Hulk comic. And what happens? Not much. The Juggernaut throws a few punches and mostly stands around waiting for Skarr to do something after that. And the fight ends with Skarr launching Juggs into space. Wow great lessen learned there. When what he should have done was use Skarr getting his ass kicked to teach him a lesson. No instead he wins the fight by BFR. Juggernaut looks bad and Skarr looks better than he is.   Then on top of that Pak continues to bring The Juggernaut up in the most dismissive ways possible several issues down the line. We get it Pak. You are throwing a hissy fit about The Juggernaut.   Combine the butthurt with some writers inability to do any basic research about the character. His motivations for one. And well. They just can't figure out what to do with him. So instead of making the stories fit the character they just change the character.   Mike Carey is the only writer that I have seen absolutely nail Cains character in years. "

The inconsistency is infuriating to me as a Juggernaut fan. I hate the writer for Thunderbolts. Juggernaut has done nothing but get his a#$ kicked. I don't understand why Juggernaut is being made to look like a bumbling fool in this series. I've never seen anything with Juggernaut where he wasn't kicking a#$ except in this series.

I think its because Juggernaut has no need to be on a team unless its off planet some where else as on earth full powered no one can really touch him & i doubt its to do with hulk more so out classing marvels gimmick for hulk of strongest there is when we all know hulk isn't the strongest .
 
 
The skaar fight was brutal to read & see Juggernaut should've killed him but no bad writing makes cain Marko look like a douche & next issue daken destroys skaar so quickly like wtf is marvel thinking .

What is more funny that he is still depicted as an unstoppable force in TB, and yet he gets hurt by a simple ninja. Next thing we've gonna see is Thor beating the shit out of him in 1 punch. Great work, Marvel.

i think juggs should be re-powered and simply given a new "role"in the MU if you understand what im saying

DC are the main writers of Marvel now. Hope that helps answer the question.