why isn't it correct to say 'poverty is the cause of crime'..
If you are asking because this is an essay question, put bluntly - you shouldn't ask other students for the answer.
Somewhere you can look for some guidance can be these books: Law in Perspective by Head; Mann and Economics, Business Ethics and Law by Mann; and Crime, Reason and History by Norrie.
I did an assignment on a very similar area in first year in Law Foundations and those books were quite helpful.