I think the problem is that Americans have forgotten the art of compromise. In all of the situations you mentioned, you have two extreme opposing sides who believe that their way is the only way and refuse to listen to any opposing view. This seems to be what is also happening in Washington today. Two centuries ago, the founders of our country were able to reach a Declaration of Independence and a constitution because they were able to listen to opposing views and strike a compromise. Until we can learn how to compromise once again, I believe that we will continue to have the problems we have today.

Lack of compromise, yes, but its more than that.  Around 100 years ago, the powers that be, whomever that may be, could make decisions for themselves without serious worry of being waggled a finger at, be it by special interest groups or by the powers above them.  It seems now, you just can't make any descision without having it picked apart, destroyed, and turned into a multi-million dollar lawsuit issue.
Might want to note as well, on the one topic I know the most about (Ystone snowmobiles) the snowmobile groups have compromised a lot, allowing guided only, limited numbers, and limited types of snowmobiles.  The enviromnental groups still won't compromise, insisting on banning snowmobiles and going snowcoach only, despite evidence that snowcoach only is no better than the current snowmobile/coach rules.

While I agree completely with both Bogator and Raven, I can't help but think there is a much more simple -- and perhaps sinister -- reason.

Money and power!  (Which, in this old world, are often one and the same.)

When you stop to look at any issue the driving force will certainly be someone trying to retain wealth and the power that accompanies it.  This was as true back in the 1800's and in 1916, as it is now.

If you will go and read the book: The Birth of the National Park Service : The Founding Years 1913 - 1933
by Horace M. Albright as told to Robert Cahn
1985 Howe Brothers Publishing, Salt Lake City 
You will see that not much has changed.  Establishing and protecting our parks have always faced the same challenges.  That will probably never change.

And one more comment about compromise, it may generally be a good thing, but there are some times when there should be no compromise whatsoever.  A great example of that was when Floyd Dominy and the Bureau of Reclamation were pushing to build a dam inside Grand Canyon National Park back in the 1970's.  Would a compromise that resulted in  a smaller dam have been a good thing?  Maybe there is another ingredient that needs to ride alongside compromise.  How about plain old wisdom? 

   Turning the other way on the question (and putting aside the media's need to foment debate), there's a reassuring aspect to all this controversy, as well: It's because a lot of people really care about their national parks, which should be a good thing.

   Nearly everyone seems to have a sense of ownership in the parks, and although I am far from the debate over, say, snowmobiles in Yellowstone (confession time: I haven't yet been to Yellowstone), I think I can see that both sides feel they belong there, whether it's on motorized skis or foot-powered snowshoes.

   So I think the question is not so much why there is so much controversy -- there is controversy because there is caring and concern -- but why it is so hard to find a solution. And here we do come around to what I learned as a journalist a long time ago: Follow the money. It is good business (for your blog, for your foundation, for your party, for your channel) to keep controversies up and solutions down. And let's face it, it's more fun to feel righteously indignant than to feel like you've had to give anything -- anything -- up.

   I also think Raven Watcher is right in that there was a time when the powers that be could whisper and get about anything they wanted. But today everyone has a megaphone -- and this site is just one of the millions.

The National Park Service organic act set rather strict standards for protection of the parks.  There will always be some who want to introduce activities that are not consistent with those standards, and they will pick a fight if they don't get their way.  However, if all their demands were met, the parks would become more like national forests or BLM public lands. 

A good question, and already some good answers.

George:
The National Park Service organic act set rather strict standards for protection of the parks. There will always be some who want to introduce activities that are not consistent with those standards, and they will pick a fight if they don't get their way. However, if all their demands were met, the parks would become more like national forests or BLM public lands.

 I don't know about introducing new amenities/conveniences.

However, there's certainly controversy over certain features, etc that predate the individual NPS units. There's mule rides in the Grand Canyon and apple orchards or the High Sierra Camps in Yosemite. The oyster farm at Point Reyes predates the park by at least 30 years. Those are going to be the tough cases.

Personally I think some people are just offended when they see something on NPS land that they feel doesn't jibe with what they think the National Park Service represents. I personally don't feel that the Hetch Hetchy Reservoir belongs, and that was created after it became a national park.

As has already been mentioned, "follow the money".
The cynic in me tends to believe that $$$$ either rules the world (or is trying damn hard to do so) - which tends to explain why compromise (in anything involving government) is non-existant.