As with everything else, there is a great deal of confusion about "voter fraud", barriers to voting, and voter registration.
Before the last general election, +Ashby Manson shared that he still receives voter registration update cards for more than one! previous owner of his house. Disturbing -- did these people sell a home and neglect to re-register? Are they then not voting? Yet, the reports of people registered in multiple states are most likely true, because voting laws vary from state to state: if one re-registers in Arkansas from Kansas, maybe one's registration is not automatically purged from the rolls in Kansas, but it doesn't happen that someone is going to drive from Arkansas to Kansas in order to vote twice on one day.
I continually, two years after my dad died, get political calls for him. He will not be voting, and the days when the Chicago Machine and Tammany Hall used names of voters to get votes who are dead are long gone.
As a canvasser, I encountered a lot of people who proudly showed me their voter registration cards. It was important to be educated in the ways and means to change their addresses to their current address or to vote in their previous district (this was within the same county), since if they voted at the polling place in their current district, but not that on their voter registration card, their vote wouldn't count, and be able to provide the forms and the process for re-registering.
There are many people who travel for work, and then there are people who are in assisted care, some of whom can't vote on their own.