Why Do I Have to Get Approved for the Google Adsense Program

It's not really about you. Google has standards to which they adhere and there are certain sites that they don't want their advertiser's ads on. Check the Program Policies for an exhaustive list of what kind of content sites are not acceptable. For the most part, they do not allow ads to be placed on any site that has excessive profanity. This is probably the hardest one to decipher as the word "excessive" could mean one thing to a publisher and another thing altogether to the Google Adsense program. To be on the safe side, if you notice more than a couple instances of profanity on a site you are considering using for the Google Adsense program, you might want to consider another site.

Sites that contain ads for beer, liquor or tobacco products are not allowed to participate in the Google Adsense program.

Sites that promote hate or racist attitudes are not allowed to participate in the Google Adsense program.

If the site you are considering promotes gambling, drugs, even prescription drugs then it is not suitable for the Google Adsense program.

A good guideline to go by might be if a site is family oriented. That may not cover everything but it's a starting place. Again, check the Program Policies for more information.