Seems like with weed it's just a matter of time but in the case of the conservative government why change it if their older voter base isn't asking for it and a portion of them would have a negative reaction if they did. I guess they think the risk of loosing some of their base is too high.
I love the work of David Nutt, who was fired from the role of Government drug advisor in the UK for trying to change the government's policies. He cited papers about how some drugs are less harmful then alcohol, tobacco and horse riding (equacy). He spoke truth and backed it up with scientific research and the Labour government fired him because it was inconvient.
https://www.theguardian.com/politics/2009/oct/30/drugs-advis...
https://www.telegraph.co.uk/news/uknews/law-and-order/453787...