Many reasons, smells better, looks better, less twisting, less cupping.
The disadvantage of cedar is at the ends. If the ends are not sealed, they'll start looking much like a paint brush. The end grain splits up into small strands of hard grain as the soft grain erodes away. If you stain this fence, you will need to seal it every year. It will last much longer if cared for properly. Seal the tops or the end grain if nothing else and it will make a difference.
That Texas sun must be hard on anything it shines on. Bare wood has no natural defense against that. You'll have to maintain whichever one you go with.