They hardly do. If they did, Massachusetts and Vermont would be weed paradises right now. They are not.
I think you may need to take a time out and do some research on how the prohibitionist movement was started here in the United States. We can discuss afterwards.
In addition, consider the states in which pot is decriminalized or legal for recreational use. California, Oregon, Washington, Nevada, Colorado, Nebraska, Minnesota, Ohio, New York, the New England states excepting New Hampshire and Vermont, Virgina, Alaska, and Mississipi.
Of those, only Alaska and Mississipi are conservative states, and Alaska has a 'high' population of Inuits who smoke the stuff for religious reasons, which skews the state further in favor than it otherwise would be.
Like it or not, pro-weed is firmly in the realm of leftydom...Except our good buddy Ron Paul of course, who favors legalizing it.