Some bastion of conservatism.
I think it says two things. For one, abortion has always been more popular among Republican voters than the pro-life lobby would care to admit and two, many people still equate legal weed with the freedom to do what you want in the privacy of your own home as long as you're not hurting anyone.
This second group will be surprised at what a public nuisance legal weed will turn out to be.
This being said, the drive to legalize weed is also a reflection of the heavy-handedness that the war on drugs had been.