The evil path gives you less benefits than the good path.
This is a very accurate portrayal of the FR setting. The moral of pretty much every novel written using the FR setting is essentially that evil does not pay, and that even when the evil side "wins," the win is temporary and will soon be reversed by the good side. Heck, the big criticism some people have of the setting is precisely that it is a "goody-two-shoes" setting. For evil-liking people, this criticism makes sense. For someone like me, I love the setting exactly for its goody-two-shoes nature.