Why are people fat? why are people poor? Why are people in such relational stress?
Not living the way God created us to is the short answer. You see people question why they can't live a certain way without experiencing negative cosequences. Whether it is health, relationships or finances if you aren't experiencing joy in any of these areas question whether or not your are abiding by Biblical standards in any of these areas and I'm sure you will see a huge discrepancy between how you are living and what God intended.
While I am not perfect in this area, anytime I encounter huge resistance I simply look at the way I am living versus what God's word says. Once I reconcile the two I experience much more peace.
If you are fat you are not treating your body the way God intended. If you are poor you are not treating your finances the way God intended. If your marriage is on the rocks you are not treating your wife the way God intended.