To clarify what is being said
People purposely lose to manage there trophy level. There are a couple of reasons to do this.
1) Finding good Matches -
Not all leagues are created the same. As you play you'll notice certain TH levels hanging around certain points. A simple reason to drop trophies is that you may have gotten so high your getting matched against players you do not stand a chance against. This happened to me when I was Th7. I would bounce in trophies allot (climb high, then drop 200-300 trophies) because when I was dragon raiding I'd get to the point where the defenses where too strong for me to have a reasonable chance of winning.
2) Loot -
a - To protect your loot. Throw your TH outside and hope a low th level will snipe it and give you a free shield (note this strategy does not require a low trophy count, nor does everything offer up there TH).
b - To find loot. There are some things you should know about loot. First off it fluctuates. Many times a player might be searching for the "sweet" spot. Second, certain ranges simply offer better choices. In gold and below (leagues) the number of abandoned bases or more casual players is much greater. Once you get to Crystal II finding a base that has a large amount of loot in its collectors is hard. This means even with the league bonus, I can find and raid more loot in Gold I than in Crystal III (right now)
3) They enjoy crushing people - Lets be honest. Sometimes we just like to flatten people for the heck of it.