It happens all over the site. Every feature that Yahoo ever added to this site, was immediately abused by those who don't care about the site or the other users. It's just how it is (same as in the offline world with people who abuse and misuse things).
Knowing why some people abuse the site or violate the 'rules' won't stop it from happening. Some Level 7s find it amusing to relocate questions. They may do it to harass the OP, the subcategory the question was moved from, the subcategory the question is moved to, or the YA Community in general.
Some do it because the question is a violation and they either are trying to hide it so it will get little attention or trying to put it somewhere they think it may have a higher chance of being reported (even though it's inappropriate to move a question for those reasons and makes them as much in violation as the user who posted the inappropriate question to begin with).
If you intend to continue using YA, you'll have to learn to live with it until (IF) such a time as we are given a reliable method to report the abuse (and I don't expect that to happen any time soon, if ever). If it troubles you that much, there are other sites online to spend time time on. You can also work diligently to reach Level 7 yourself, and thus gain the ability to relocate misplaced questions that you didn't post yourself (there are a number of Level 7s that do that as well).