Because Nickelodeon sucks.

Because they are so commercialized. =(

Kids shows are being influenced by popular media. Haven't you noticed the explosion of "action cartoons with insane violence" after the release of movies like "The Matrix"? Sure, there was violence beforehand, but the amount of violence and fighting a la "The Matrix" has skyrocketed since these types of movies have come out. And it's not just violence. Rather unclean humor has become a regular member of the new summer blockbuster, and you see the result in many new children television shows. Granted, due to the fact that it's for children, the humor is watered down a bit in crudeness, but it's still obvious that it's all related. I believe that this could be a good thing, actually. Children are getting more and more access to material meant for adults. I don't know about many, but when I was a kid, and I saw the latest "adults only" thing, I thought it was cooler than anything we had. By bridging the gap between these two things, it might help minimalize this effect, but how far can we go? Will we start to see blood and guts in children cartoons? Male anatomy jokes? This also has a bad effect. By bridging this gap, we're making a sort of homogenous pool of material, and soon, watching the latest kids cartoon could possibly be a series based off of Kill Bill :-X People won't really care what their children watch, as it's just as bad as the stuff they're SUPPOSED to watch. Of course, this is like a 350+ years down the road schedule, that is if we survive that long. It's a double-edged sword, but I don't think we can expect much to change. Big commericial companies control these things, and all they wish for is money. They could give a rat's ass about your children.

Because the good old days are gone when quality children's programming actually was an important issue. A lot of the new ones I see would make me shudder to watch if I was a kid back in my day.

For starters, there are people who disagree with your opinion. Anyway, the answer is MONEY. People want money nowadays. Sure, call it greed, call it selfishness. That won't change that people nowadays do want money. (Note: "People nowadays do want money". I do think that this generalization is a fair generalization to make. People do want a roof over their head, food on their table, and so on. How do you get there? Well, with money, of course)!

Because the creator's, writers, and producers of said shows don't attend church.

Becuase it's a filthy world.

dr.maxwell blames it on the decline of the western civilization.

Money is the priority nowadays. They want to make the simplest thing, just copy the same themes, with the cheapest animation, and if you can do it to sell toys or accessories to the show, even better. The people in charge of making them also don't have the values of the past or they feel TV isn't the place to teach such things. They make whatever the greatest number of people will watch for the least amount of money and effort.