Because you need a large enough number to actually make a difference. 1 person going from place to place voting over and over could only get a certain number o

Because you need a large enough number to actually make a difference. 1 person going from place to place voting over and over could only get a certain number of votes in over a few weeks. Could one person put 200 votes in if they really worked at it? Maybe, but realistically 200 votes just won't do it. You basically need a conspiracy.