From what I understand I'd say it is questionable that voters made a conscious effort to get rid of de Gualle.
With Churchill, it was really a combination of factors. Most important was that the Great Depression and WW2 had caused huge economic difficulties for people whilst opening their eyes to how powerful the state could be. Many saw the resources that the state had mobilised to fight the Axis, and wondered why the government couldn't make a similar effort to improve living standards. They wanted a welfare state, but the Tories, who had by this point been in power for fourteen years (including through the depression) weren't seen as an old force incapable of delivering that.
On the other hand, the war helped to turn Labour into a credible force for government. Their leaders had served in the wartime government, which used an awful lot of state intervention to keep the war effort going, so the country was a lot less wary about a government that valued collectivism and the state taking a role in the economy.
There were also factors related to Churchill himself. Whilst he was widely seen as a war hero, that didn't mean everyone thought he would be a good leader in peacetime. His remarks where he compared the Labour opposition (with whom he had served in government) to the Gestapo hurt him and confirmed many people in their views of him.