because, they didn't vote in 4 years.
Wisconsin lets those folks, and anyone, to register online.
You can register to vote and can also get a mail ballot at the same time.
You'll need;
1) Your WI Driver's License, a Wisconsin State Id number
Make sure your name matches whats on the ID, no nicknames. So for the 18 yrs old Agnes, whose been called Buffy since birth...you name is Agnes. Use your real legal name, or you will be rejected.
Check it out...
myvote.wi.gov