The problem is that when you knock at a door, sometimes you get an enthusiastically supportive response or sometimes you get a quite strongly expressed negative response, but I would say that in many elections you get the undecided, and there are shades of undecided: “Well, I'm interested”, or “I'm leaning...”, and so on. This would come down to the nomenclature of how parties would be required to log the face-to-face contact they're getting and how to express it to people without being either offensive, or as professor Pal suggested, subjecting them to vexatious inquiries for days and days just as a time-consuming, resource-consuming exercise.
On October 2nd, 2018. See this statement in context.